I dont think there's anything special about seduce scheme like the murder one has, so you probably need to just look at character interactions and maybe scheme itself because i kind of suspect that to make them more common you would need to relax AI triggers, not just decrease months per check... I'll point you at files coz the script is ancient and it calls the scheme "courting" for... reasons.
EXCEPT IT DOESNT! Im 99% that got changed at some point, i swear it was confusing, sorry for pointing in the wrong direction, it is actually just seduce and i corrected everything below.
So, you need to look at common/character_interactions/00_scheme_interactions.txt just ctrl+F for seduce_interaction, you can maybe broaden the ai_targets list but that requires knowing what lists there are in the first place (info file in the same folder has them i think), you can lower ai frequency, which, despite it's name, refers to months per check, not checks per month or smth, so higher "frequency" = less checks, and finally you can dig in the is_shown, ai_potential and ai_will_do (the last one is chance of them clicking it if they can... i think, so raising that one is good)
There might also be some ai specific restrictions in the scheme itself which you can found at common/schemes/scheme_types/seduce.txt