That bonus to Max Health doesn't do anything until you activate a buff for it to affect. You probably activated Martial Arts Initiate which gives a 70pt buff to Max Health which that 8% bonus can affect making it a 75 point buff. Vitality also gives a bonus to max health. If your Vitality is at 8, as it is with most archtypes (unless you've been putting points into it), that would give another 6% bonus making it a 14% bonus total making that 70 points Max Health buff go up to 79.
You can check all of that in the bonuses tab of the status window (P hotkey).
Bonuses only affect active styles, buffs and upgrades: which show up as icons under your hotbar. That's one of the most important concepts of the combat system to understand. So if you don't have something active under that hotbar giving a buff to Max Health, the bonus has nothing to work on.
The Max Health bonus will affect Health Boosters. Patcher's Health Buffs get stronger from their own Max Health bonus.
