That was my first thought, but in testing, everything used the 41. I cast the spell on a monster that was engaged with my other character, and had another monster next to it. The hit on the main monster used a 41 accuracy, and then the sickening effect on my character and the other monster also showed an accuracy of 41.
Everything I tried, all results showed it used a 41 accuracy, never a 38. It isn't a big deal, but I am curious is this a bug in the tooltip or am I misunderstanding something?