Progressive damping isn't really a thing. There was a time where a company sold pistons with tapered pins that varied the flow based on shock position... but generally speaking, the "factor you need to consider" is piston speed not piston position. Also, what might be more important, is piston direction. Recently I've seen released valved pistons, which mimics what you find in good real shocks, where there is a seperate compression and rebound circuit.
Progressive springs.. are also not commonly used. They show up more where travel is insufficient. On real cars, they have snubbers which act as rising rate bits of the suspension. For us, that's just going to be the foams in the tires compressing.
This.. is something you should pick up suspension tuning books on. :-) The rules are the same weather it's 1/28th scale or 1/1 scale.