Ok... I think by 'attacks' you mean dice rolls tomkaz...? Spells like fireball/skull trap do not have 'attacks'.
I'm not sure if I'm comprehending your post correctly as you're using rather unconventional terminology, but I think the problem here is that you have a very, very different understanding of how spells work in this game than the way it actually does. In your example you have a level 7 caster casting skull trap. Each hobgoblin within range of the spell (keep in mind skulltrap doesn't have a very large area of effect) takes 1d6 (average 3.5) x 7 dmg (average 24.5) from the spell, half of that if he made the save, which is about 12 dmg.
Sounds like (based on your description it's not clear whether the fireball was cast by someone else or the same guy, I'm guessing same guy) the next round the bard then cast fireball. That's another 7d6 (average 3.5x7) fire damage. Exactly the same as the skulltrap, on average, in this example.
Whether the spells were cast in the same round or over 2 rounds, the total damage is going to be around 24 dmg on average if both saves are made (quite possible if a hobgob is lucky enough). If he saves vs one but fails one he takes about 36 dmg on average; if he fails both then he probably dies after taking 48 dmg unless he chugged a potion in between the two spells OR if the rolls were much lower than average (which is entirely possible). A hobgob captain that has 40 HPs certainly could survive these two spells cast by a lvl 7 character.
I hope that helps; it sounds like you're expecting the hobgob to eat anywhere between 70-140 dmg between the 2 spells, which is probably not going to happen at lvl 7. The worlds unluckliest hobgoblin that failed BOTH saves vs MAXIMUM possible damage of the 2 spells cast by a lvl 7 caster would take 42+42 dmg. In that case, yeah, he's dead, but that's one heck of a bad day for him, good day for you; the odds of this happening are mathematically extremely low.
As for SCS's component that caps skulltrap dmg at 12d6, it currently has no effect even if installed in your particular example since you're taling about a lvl 7 caster; you won't see it impact your game until you're dealing with casters that are ABOVE lvl 12, whether yours or enemies.
Choosing to install or not install this option is very clearly laid out; you do NOT need to edit tp2's or whatever you're doing, as SCS will ask you during installation whether you want the component installed or not if you're installing manually.
If you're using BWS to install, then you have to check or uncheck the corresponding box next to the listed components of SCS (there are quite a few, it's possible your tired eyes didn't see it) in the mod selection menu/screen, which I think you know about already.
Hope that helps clarify things.
Edited by Ithildur, 09 February 2016 - 07:53 AM.