Spell pen has in its calcualtion spell level. So for a lvl 20 caster you would get 20.

If you have 17 clr 3 monk you have spell pen of spell lvl 17

If you have 17 clr 1 wiz 2 monk, am i correct that the spell pen form this is 18?

(obviously this is only part of the total spell pen calcualtion)