User blog comment:HQDominator/Highest Possible HP in Brave Frontier Global/@comment-26455864-20150722174631

I think all boosts to any stat are additive, which would include spheres. I believe this would actually make Colt's max HP (with everything being the same as what you described) 32182.5 HP. 100% + 15% + 80% + 30% + 50% = 275% boost

I'm not quite sure how the arena rule works though, so I may be wrong.