Scaled boss HP across skill levels

[Naphtha]

I know that with each skill level, the bosses seem to become a lot more durable, but I've been meaning to ask if we ever figured out exactly how it's calculated. The answer should help out a lot with the single player level pack I've been working on.

Boss HP, according to the .HAM files for Counterstrike and Vertigo as viewed through RbotEdit:

D1 L7 Boss = 4000 (an alternate version with 5000 HP is in the D2 data, but not in any mission)
D1 Final Boss = 7000
Red Fatty = 2750
Water Boss = 3250
Magnacore Boss = 3750
Ice Boss = 3250
Alien 1 Boss = 4750
Alien 2 Boss = 5500
Vertigo Boss 1 = 2750
Red Guard = 5500

It seems like the jump from Hotshot to Ace is the real difficulty threshold when it comes to how much damage the bosses can sustain. Offhand, I think a regular showdown with the Alien 2 Boss on Hotshot takes roughly four or five Shakers and maybe a couple Smarts at the most, but on Ace it seems to take roughly double that... and I haven't tried on Insane yet, so I don't know how that would go.

I'm planning on four custom bosses for my mission pack, which also features slightly rebalanced weapons (for example, Level 6 Quads are as strong as Level 4's from D1 and the Spreadfire has its D1 speed, while the Helix was dropped from 55 damage per round down to 45). I had a rough estimate in mind for the boss AI's and HP: the warmup Red Fatty would have 2750 HP, the wake-up-call Alien 1 Boss 3500 HP, the slightly-less-dangerous Ice Boss 4250 HP and the modded Alien 2 Boss would have only 5000 HP to make it go down a little faster. But how much of a difference would that actually make on the two hardest skill levels?

[Xfing]

500 hp per boss is not a great difference, especially seeing that there'll likely be many invulnerabilities to take advantage of. I have also noticed that bosses gain in durability on higher difficulties (though the D1 final boss always seems to take forever to go down, and for good reason). I don't really know where to look to find out the exact calculations, but since there's only one value given in the HAM, then I guess it simply boils down to percentage.

[Sirius]

Might mean one less shaker... it's only 10% less though (actually not even quite that). It wouldn't be obvious if you weren't looking for it I don't think.