Okay, here's how the spreadsheet does it (this is Jonathan Dale's spreadsheet from November 2003)...
- Essence RR = 3 x Em + Racial Essence Bonus
- Channeling RR = 3 x In + Racial Channeling Bonus
- Mentalism RR = 3 x Pr + Racial Mentalism Bonus
- Arcane RR = Em + In + Pr + Ractial Essence Bonus + Racial Channeling Bonus + Racial Mentalism Bonus
- Ess./Chan. RR = Em + In + Racial Essence Bonus + Racial Channeling Bonus
- Ess./Ment. RR = Em + Pr + Racial Essence Bonus + Racial Mentalism Bonus
- Ment./Chan. RR = Pr + In + Racial Mentalism Bonus + Racial Channeling Bonus
For all of these there is a +15 bonus for "own" realm, but it only applies to one realm for "pure" spell users (e.g. a Magician gets a +15 to Essence, but no bonus to Ess./Chan.). Hybrid spell users are given the +15 bonus to their hybrid realm
and to the contributing realms individually (e.g. a Sorcerer gets the +15 to the Chan./Ess. realm
and to the Channeling realm
and the Essence realm).
Again, this is the way the spreadsheet formulates the RRs, but I honestly can't find anything in the RMSS books that disputes any of this. Not to say it's absolutely balanced or fair, but that does seem to be the way the rules are presented. I could very well be wrong, though.