Okay I guess I will take a step into this...Try to think in leverage terms, The longer the lever the less effort and the shorter the lever the more effort is required... Also if you have driven various length vehicles then you have noticed that at some point the suspension and length of frame have a direct effect on each other.
Hope this helps
OK the length of suspension travel must be constant and if you do not keep that constant then you will subject your suspension to either under or overextension also the work load that you put upon your suspension will be affected by length of frame, lever. A short frame will cause the suspension to work harder as the front and rear are closer together and a longer frame will not as they are further apart. Think about speed bumps as your front suspension raises and loads it will transfer weight to the rear and the rear will do the same to the front and vice versa as it unloads until the vehicle is on a flat surface where the suspension becomes static.