I like how Twoy's
formula makes lower-HP units more capable of having a high Attack/Defense than high-HP units, thus providing a neat balance between small punchy units and gentle giants ...
... or does it? That HP^2 is kinda brutal, but then again it's offset by being divided by 8.
Btw, let's see how the Diwigible fares with this formula. (From memory: Diwigible had 50 HP, 21 Attack , I'll need to make it move 5 as it's a flier, and might as well put in defense 5.) 2500/8 + 26/2 + 2500*5/2 + 0 = 312.5 + 13 + 6250 = 6575.5(!!).
Who needs HP caps when the ^2 effectively makes a unit impractical cost-wise soon enough?
It's actually too effective for the purpose, maybe?
But it looks ok ...
Just for kicks, here's another formula and justification:
Big units have many HP, so we associate HP with unit mass. A large mass is harder to move, so Move and HP are antagonists. Defense is also antagonist to HP, to a lesser extent because ...
Remember that mass increases with the cube of size, strength increases with the square of size- just like area, which is what you have to defend. This might suggest some different kind of capping, where Attack would be capped by (Hits^(2/3)). And also since units that are large have more of themselves to defend, they find that more expensive to do.
Finally, we can debate whether Defense should be antagonist to Move (armour) or supportive (dodge). So, let's pick the middle and make it neither.
This yields a cost formula like this-
Hits*Move*Constant_1 + Defense*(Hits^(2/3))*Constant_2 + Attack + Special,
where Constant_1 and Constant_2 are selected by some rule of thumb.
Say you want Move 2 to be "normal", then Constant_1 is 1/2, and units with this Move or less don't need to stress themselves too much on account of being fat joggers.
Now, say you want Defense 2 to be "average", then similarly Constant_2 is 1/2, and units with this Defense or less don't employ any special techniques/armour to keep their hide intact.
And a reminder, by this logic, Attack is capped at Hits^(2/3). Learn to love the Calc!
The whole point of this is lost if you keep it a secret.