Let's say a skill heals for 15% Max HP without any points into upgrades.  And then you upgrade it and it gets a +10% Heal buff.  I understand that the calculation is 10% of that 15, totaling 16.5% Heal for the skill. 

I am wondering if this method of calculation is the same across the board for all types of skill upgrades.  Let's use Warmaiden as a new example.  Crumbling Blast has a 75% of placing a debuff.  After the skill is upgraded and gets a +10% Buff/Debuff Chance, does this mean that the chance of applying the debuff is now 82.5% (as a result of adding 10% of 75), or is it now 85% Chance (as a result of straight addition)?