True porpoising is (I believe) due to shot shocks. When the front end accentuates the effect of a series of dips in the road surface, that is usually a) somewhat intended by design, and b) a good thing. A properly operating shock should dampen greatly, but allow rebound of the spring to above its static height, so if, just as the rebound reaches its apogee- you enter a new dip, the coach has farther to fall than on a flat road entering a similar dip. Then the impact of the new dip is greater than it would otherwise be. But that is a function of the road surface and travel speed, not the shock. The shock is either good & doing its job (no porpoising after a single dip, BOING, Boing, boing, or the coach settles down rapidly after syncopated dips*), or there is porposing.
W/that said, I have nothing to add about your real question. Koni's have been discussed here before; try a search on "koni."
(*not to be confused w/acapella groups)
Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project