Wait now that you brought it upoooooooh
What is the percentage/fraction? I.E. Ingrain is normally 1/16; what is it boosted to?
Cradily's max HP is 124
None Big Root Ingrain did: 7/124 = ~ 5.645%
Big Root Ingrain did: 9/124 = ~ 7.258%
22.2% increase
+
Ferrothorn who has 116 HP
None Big Root Ingrain did: 7/116 = ~ 6.03%
Big Root Ingrain did: 9/116 = ~ 7.758%
22.27% increase
+
Amoongus who has 182 HP
None Big Root Ingrain did: 11/182 = ~ 6.04%
Big Root Ingrain did: 14/182 = ~ 7.69%
21.4% increase
And 6.25/8.25 (the 4th gen none-big root, and big root respectively): 24% increase
So the above numbers are probably due to lower level/HP and rounding down, i.e Ingrain healing with or without big root probably hasn't changed from 4th gen.