Modifiers are multiplied ([1+Mod1]*[1+Mod2]*...) not added so optimal wing size (in numerical way) doesn't increase with positive modifiers. Exact equation for optimal wing size is:
x = (SP+1) / (2*SP) - for air to air battles
x = 1 / (2*SP) - for bombing missions
SP - stacking penalty
x - optimal numbers of wings
So in your examples:
8% means 6.75 wings for air to air and 6.25 for bombing
2.5% means 20.5 for air to air and 20 for bombing
Modifiers multiplication also means that your efficiency will always be zero or lower if at standard 10% penalty you have 11 wings for air to air battle or 10 wings bombing something. Nothing in game can change that.
If the modifiers are multiplied you are correct.
The modifier would "only" make a (big) difference for the effect of the optimal stack than.
But I see no difference between air to air and bombing - the optimal number of should be (1 + SP) / (2*SP) in both missions. What am I missing?
I am not sure I understand the calculation above. If you stacking penalty is called SP, then your strength function is
(1-SP)^x
If we call (1-SP) = a, which numerically is 0.9, then we have that the derivative is
d/dx a^x = ln(a) a^x,
where ln (0.9) = -0.105. This derivative is not zero for any positive x. Thus, no optimum exits. You always gain strength by adding planes, but your attack per plane is largest for the first one, and drops as you add them.
This is the entire point! I think originally there was a bug in this calculation (which I hope has been fixed now), where the strength was calculated as
(1 - SP * x) instead of (1 - SP)^x, which clearly leads to some mathematical issues.
I am not sure I understand the calculation above. If you stacking penalty is called SP, then your strength function is
(1-SP)^x
If we call (1-SP) = a, which numerically is 0.9, then we have that the derivative is
d/dx a^x = ln(a) a^x,
where ln (0.9) = -0.105. This derivative is not zero for any positive x. Thus, no optimum exits. You always gain strength by adding planes, but your attack per plane is largest for the first one, and drops as you add them.
This is the entire point! I think originally there was a bug in this calculation (which I hope has been fixed now), where the strength was calculated as
(1 - SP * x) instead of (1 - SP)^x, which clearly leads to some mathematical issues.