All damage types are defined under <YourRimworldPath>\Mods\Core\Defs\DamageDefs\ if you want to see how much default damage they do, who they do it to, and how they do it.
I don't have a lot of experience with buildings, but I believe IDE's use the CompProperties_Explosive class to achieve the desired effect when sprung. You can try to use damageAmountBase to modify how much damage you want it to do, but I'm not sure that is valid as I've never tried to use it under CompProperties_Explosive. Otherwise, you could use the BombSuper damage def and lower the explosiveRadius. If BombSuper is too powerful and damageAmountBase doesn't work then you might just want to define new damage types so you can set it exactly how you want it.
As for the whole 3.9 thing I don't have a good answer for you, I've been using ranges that way and mentally rounding it up because I figure there's some reason for it even if I don't know what it is. Anyway, going from 3.9->2.9 shouldn't mess with anything unless you are using damageFalloff.
I don't have a lot of experience with buildings, but I believe IDE's use the CompProperties_Explosive class to achieve the desired effect when sprung. You can try to use damageAmountBase to modify how much damage you want it to do, but I'm not sure that is valid as I've never tried to use it under CompProperties_Explosive. Otherwise, you could use the BombSuper damage def and lower the explosiveRadius. If BombSuper is too powerful and damageAmountBase doesn't work then you might just want to define new damage types so you can set it exactly how you want it.
As for the whole 3.9 thing I don't have a good answer for you, I've been using ranges that way and mentally rounding it up because I figure there's some reason for it even if I don't know what it is. Anyway, going from 3.9->2.9 shouldn't mess with anything unless you are using damageFalloff.