Question about +stat buffs on familiars

Its by summon ranks, the higher the rank the more it can give. But then that means theres like 3 variations, (small, medium, large). I'm kind of lazy to look into it too much but a rank 1 and rank 2 large healing is clearly different. Red wyvern is about 15% hp, and Mutant snail is about 25% hp, tested it myself. Problem is it screws up when theres potion lock though.