aah, wait, so: PF1 basically uses the CL/2 progress, isn't it? (plus ability of course)
I just checked it in FG: The base DC approach is for both rulesets, 3.5e and PF1, similarly coded. So, ability plus spell level. You need to switch to the CL/2 approach for the spells, then you should get the correct progression and the CL effect will affect it correctly :)
Pheew, nothing to fix on my side :D

