Question about adapting spell guidelines

Hello everyone,

a long time ago, I read somewhere some rules about how to adapt the spell guidelines from one form to another. I am not entirely sure but I think it was in some sourcebook as they were official. I've been completely unable to find them again so if somebody could guide me to the right place I'ld be very grateful.

Thanks and have a nice day.

I believe some of the samples spells/items in "Hermetic Projects" use guidelines extrapolated from unrelated Form/Technique combinations.

Specifically, I think they were most prevalent in the 'Volcano' and 'Tower' chapters...