For a magus with giant blood, do Range Personal spells need to account for the larger size? Would Flexible Formulaic Magic help out in such a situation?
Corpus spells operate on individuals of up to size +1. If the target goes beyond that then the spell design should take it into account.
I think it's within the spirit of Flexible Formulaic Magic to allow for an increase in the target size. You're allowed to increase/decrease the casting level of the spell by 5 to increase/decrease any one of range, duration, and target. For my money, +1 magnitude for size is within the bounds of increasing the target parameter by 5 levels.
And I agree. As both a player of a magus with FFM, and the former SG of a saga with an PC magus with giant blood thinking himself virtually immune to all T:Ind corpus spells.
In the first case yes if it is a Corpus spell and arguably also for Mentem.
2nd case, yes.
Size doesn´t have effect in Mentem with Part or Individual Targets, only in Group or other masssive and multiple Targets.