I would put medium at +- ET max health 156, light at ET's 120 and heavies around 200. Fewest bullets needed to kill a medium at close to semi close range, without missing: 4. Of which 3 headshots and 1 random hit or 5-6 torso shots or 10-12 feet/arm/leg/hand shots.
Note (1) that close to semi close range is consider as standard in this case. Bullets drop damage over range.
Note (2) 36 health difference is really a lot in that game, especially in 1v1 with someone that has 156 health.
That is what I would like to see. I'm pretty sure that it will be balanced in another way.