I have an Incantatrix and I am interested in getting the build
Wizard 5/Incantatrix 3/Nar Demonbinder 1/Ultimate Magus 10/Incantatrix 4
as suggested in the famous Ultimate Magus Handbook
However, I have doubts about something: caster level.
The character’s caster level is equal to his Nar demonbinder level plus his levels in one other spellcasting class of his choice.
As far as I see it, the feat Practiced Spellcaster is not needed. Not only that, the CL explodes. Let us assume Wiz8/ND 1/UM X.
at X=0: ND has a CL of 9, wiz 8.
X=1: wiz spellcasting is increased by one, making it wiz 9. now ND has CL 10. (to that we add Arcane Spell Power after all calculations are done, but let's ignore that for the moment, it's the same for both classes anyway)
X=2: both are increased - wiz 10 and ND has its CL at 12 now.
X=3: wiz is at 11, ND has 1 base and 2 from UM, i.e. CL is 14.
X=4: wiz is going to be increased to 12, ND stays at 3 spell levels known, but his CL also get another bump to CL 15 (and again, arcane spell power makes this an effective CL of 17).
And so on
According to my understanding, wiz will always be the class to be bumped by UM at levels 1/4/7/10 and the CL of wiz with Arcane Spell Power ends at 23, and that of ND even at 30(!)
What do I misunderstand?