[Gameplay] Biscuits heal you for 15.5% missing health instead of 15%

Reproduction:

1. Buy a lot of HP so you diminish the effects of base hp regeneration.
2. Don't buy base hp regeneration
3. Go low hp so biscuits can regenerate more hp.
4. Activate the biscuit
5. When the biscuit finishes make some math.

This is my math: i had 5301 max hp, 500 current hp, 23 base hp regeneration per 5 seconds
15% of 5301-500 gives 720.15 (Biscuit Hp Max regen) over 15 seconds the base hp would give me 69 hp
720.15+69+500=1289.15 (rounded to 1290 in game) I actually reach this number, but just before i say "oh ok it gives 15% hp" the biscuit gives me another tick of heal making me reach 1316 hp
which is 15.5% of 5301-500 = 744.155 base gives me 71.3 hp
744.155+500+71.3=1315.455 (rounded to 1316 in game)
Which is the final number i reach, after this my hp only regenerates for 2.3 hp every 0.5 seconds

Tried this multiple times and reached the same value.