Suggest tuning duration (both base and extend value) instead of capping it. 16 seconds base plus 16 seconds extend duration if not amplified, shifted right by the amplify count.

It is effectively a one-off unexpected vanilla behavior. Since it works on health/tick, anything past 6 is 20 hearts a second (while regen 5 is 6.67 hearts a second). With invulnerability frames on hit, you would need to basically be insta-killed. It just isn't reasonable to have that much regen