Have you stopped beating your wife?
Now, if I have indeed inverted the concept, why don't you show me how you think it should be done properly so I can tell you how you are wrong?
If we're comparing the opportunity cost of Mia (or anyone) getting 350 Bexp in C8 and Zihark (or anyone) getting 350 Bexp in C12, the former cannot be less than the latter. Mia's Bexp must come from Chapters 1-7. Zihark's can come from chapters 1-7 or it can come from chapters 8, 9, 10, or 11. Bexp from these later chapters is strictly less valable than Bexp from chapters 1-7 because C1-7 Bexp can be used in all of the ways C11 Bexp can be used - and more.
I think you mess up oppportunity cost. Remember, best alternative forgone? It doesn't include saving it for later use unless you think Marcia isn't getting enough bexp from what you earn in chapters 8 to 11 (since she mainly needs it for chapter 12, maybe unless you are going for ridiculous turns that Cynthia isn't allowing anyway). Now, if you think saving it for Marcia instead of using 350 on Mia is the "best alternative forgone", then fine. Do you? Also, what do you mean "cannot be lower than the opportunity cost of c11 bexp?" That bexp can go to Mia or Zihark. If you dump 400 bexp on Zihark in chapter 12 (not 11, btw, as Zihark is still an enemy during the base, yes?), then you can dump 400 on Mia instead. The op. cost is whatever it is. The cost for c8 could be lower or higher or whatever depending on what you think the best use of it in chapter 8 is.
Concerning the opportunity cost of 350 Bexp in C8, I don't know what it precisely is. It might be giving more to Boyd or Oscar, it might be saving it to give to Marcia. It might even be giving it to Jill. Whatever the case may be, the opportunity cost of 350 Bexp in C12 must be lower, because we now have more total Bexp to give to their most valuable recipients. We've already given the Bexp to, for instance, Boyd or Oscar or Marcia, or saved it for Jill. So the next best use might be giving it to Kieran or giving more to Marcia/Jill, or saving it for Astrid/Makalov.
I agree. But if we give Zihark 350 Bexp in C12, it can be from the less valuable C11 and/or C10 Bexp cache. Capiche?
That's the most insane thing I've heard in a while. Higher in c8 than in c12? You are saying that it is a lower op cost to save 350 bexp from chapter 8 all the way to 12, and not use it until then, than it is to just give it to Mia? Best alternative forgone. The op. cost is the SAME. Whatever you do with that 350 bexp in chapter 8, whether you give it to Mia or save it for Zihark, the best alternative is whatever the best alternative is. It doesn't change.
Both units getting one or the other's optimal resource bundle is a fine approach when comparing units with similar availability and similar (enough) optimal resource bundles. It is a poor approach when comparing units with very different availability and/or very different optimal resource bundles. (I would not recommend it in a Mia vs. Geoffrey comparison. I would in a Mia vs. Zihark comparison.) No matter the comparison approach, Mia must be penalized for the resources she receives in excess of Geoffrey. Likewise with Zihark, if you so choose to compare them with different resource bundles.
So I'll bring up Mia and Geoffrey again. Do you think if Mia gets 1000 bexp during her life until chapter 25, that Geoffrey is entitled to 1000 bexp before you can make any comparison to Mia? I find that nuts. This "each unit gets optimal resource bundle" thing is stupid. That's all I'm trying to say.
You contradict yourself: "The op. cost is the SAME. Whatever you do with that 350 bexp in chapter 8, whether you give it to Mia or save it for Zihark, the best alternative is whatever the best alternative is. It doesn't change." But, as I explained above, an amount of Bexp given later is necessarily less valuable than the same amount given earlier.
Where did I ever say it's free? Granted I suggested the cost is negligible, but for those that weren't happy with it I proposed a compromise where Zihark gets a portion of Mia's bexp but not the whole thing because of the cost of saving that bexp for chapters.
All else being equal, Bexp used earlier is more valuable than Bexp used later. Don't you see: that also increases the opportunity cost of using Bexp earlier! C1-7 Bexp can make Boyd or Oscar more valuable in chapters 8-11 (and more). C11 Bexp cannot. C1-7 Bexp can be used in all of the ways C11 Bexp can be used, but the reverse is not true. Therefore, C1-7 Bexp is more valuable than C11 Bexp - it has a higher opportunity cost. If Mia takes 350 of the former and Zihark takes 350 of the latter, we pay a higher opportunity cost in the former scenario. (But, I repeat myself.)
And If you think I inverted PV/FV, then you need to re-read what I said. Or I'll try to reword it. Mia is the bank. You'll notice that Zihark's 500 bexp doesn't earn you interest or anything. Mia earns you interest because she uses it. This would be a completely different story if you could earn interest on bexp held from chapter to chapter. Which would be awesome, btw. I don't get how you think this is inverting when Mia is the 500 now, and Zihark is the 500 in 4 chapters. We know from PV/FV that money now is better than money in the future, and so giving Mia 500 bexp is worth the investment because she gives us 500(1+i)4 value for that 500, whereas Zihark gives us 500 value for that 500. The cost is the same exact number, 500. To use it early it gives bigger gains. That much is also intuitive from the playing of the game. "Mia can make contributions before Zihark joins, and those should absolutely be factored into a comparison between the two units..." So we are agreed.
But all else is not equal when we consider the value of Bexp when used. The recipient of the Bexp determines the value of the investment. Would you agree that it is more valuable to give Rolf X Bexp in C9 instead of saving that X Bexp to give to Marcia in C10? Of course not - that would be absurd. But that conclusion would be warranted from your naive application of PV/FV. If I'm understanding your application correctly, Bexp given earlier provides a greater investment than Bexp given later by virtue of it being given earlier. What a unit can actually do with the Bexp is not considered in your analysis.