The general ReVi spell that protects against supernatural creatures with a Might less than or equal to the level of the spell has the parameters Touch, Ring, Circle (total modifier = +3 magnitudes)
Does changing the parameters affect the Might level that the spell protects against directly (e.g. choosing lower params means it protects at level of spell +5 or something) or indirectly (e.g. still just protects at level of spell, not matter how params are changed).
How would the Might level of protection be affected for a spell with the parameters Personal, Sun, Individual (total modifier = +2) or Voice, Sun, Group (total modifier = +6)?
I must admit to being a little bit confused at the question, so I am not sure that this post is on the right track.
You can change the parameters as you prefer them, but I think the Might protected against stays the same as long as you do not add or subract levels beyond the 3 magnitudes added to get the Gen ReVi Touch/Ring/Circle version. In effect you could create a Personal/Month/Individual spell protecting against the Might equalling the spell level (A concept that has caused many discussion on the power of Wards).
This might best be cooked down to say that at Base level (Per/Mom/Ind) a Rego spell can protect against a Might 15 creature.