OK, i did many tests.
Without light arts :
Base = 40hp/tic
Base + Musa(max) = 65hp/tic
Base + Bookworm's cape(max) = 50hp/tic
Base + Arbatel Bonnet +1 = 47hp/tic
Base + Musa(max) + Bookworm's cape(max) = 75hp/tic
Base + Arbatel Bonnet +1 + Musa(max) + Bookworm's cape(max) = 82hp/tic
With light arts :
Base = 64hp/tic
Base + Musa(max) = 89hp/tic
Base + Bookworm's cape(max) = 74hp/tic
Base + Arbatel Bonnet +1 = 71hp/tic
Base + Musa(max) + Bookworm's cape(max) = 99hp/tic
Base + Arbatel Bonnet +1 + Musa(max) + Bookworm's cape(max) = 106hp/tic
It seems there's is a bad translation on the Arbatel bonnet +1
It's not 15%, but a flat 7hp additive
and if you go on the bg page of the original Abyssea head SCH :
Svnt. Bonnet +2
we can see that each regen tiers spell win 1 hp/tic, with 5hp/tic for Regen V.
I think they augmented the Arbatel Bonnet lvl109 with +6hp/tic and the 119 with +7hp/tic