Regneration Bonus

Say, for instance, that a player with r7 Rest (400% Stamina rate) sits at a rA Campfire (200% regeneration rate).

Would this result in a 600% faster stamina regen (additive) or 800% (multiplicative)?

Judging by the rate that I recover stamina with my rA rest and r9 camp, it looks to multicative. rA is 325%, or 1.3 stam/second. Combined with a r9 campfire, 250%, that equals 3.25 SP/sec.