Ram recoil
Recoil per tier is parity 3 × (their weight ÷ your weight) ^ 1.5, capped at 12 per tier. Ram something your own size and recoil is what it always was; ram something much bigger and it climbs steeply toward that cap.
Ram levels no longer buy safety, only damage — a level adds 1 to your own displacement, which nudges the gap in your favour, but that is a rounding effect and not the mechanic.
The parting blow
Fleeing successfully still costs a parting blow, and that blow now scales by the same weight ratio the ram reads — running from something much bigger than you costs more than running from something small. It is not clamped away from lethality; it can still sink you.
For scale
Sloop 10, Brigantine 20, Galleon 30 — displacement units. Reef Shark 8, Young Serpent 7, Diving Serpent 14, Shellback 16, Siren Spitter 12, Kraken 30, Leviathan 36.