I like the idea of two different jumping actions (one for splat height or above, another for below splat height)!
This adds some variability to the object (and thereby increases its potential range of application), without resulting in too much complexity (both from a coding and a player standpoint).
If I remember correctly, both in L2: The Tribes and in Lemmings 3D, the trampoline’s range gradually increases with fall height. Lemmings 3D showcases this immediately on the very first level, “Take a Dive”. That would probably be a step too far, since it would also be difficult to predict the jumping range without object skill shadows for Fallers — and as far as I’ve understood you, you deliberately don’t want to include skill shadows for projections of regular movements, such as walking / falling (as they would also be relevant for, among others, Radiation and Slowfreeze)