changing from one frame manufacturer to another.. and using the same njb tricshoxs which were perfect on the old frame. on the new bike the mounts mean the shock is markedly more 'laid down' and although the bike 'sits' at the right height 'unladen' once my weight is on it the spring compresses almost to the stops.

does laying the shocks down make the spring action softer? do i stiffen them up and or lengthen the shock at the same time. given the price of a pair i only want to do it once...

You could always just change the springs ?

The change in position will be the problem. The more lean, the higher the spring rate.

No idea what rates are available for your shocks but as a guide, on Falcons, more upright shocks like early Ossa MAR (in the conventional position, not moved up the swingarm like a Fantic or later twinshocks) would use 50lbs springs for an average weight rider, whereas a later MAR or Majesty with laid down shocks would use 60lbs.

Try preloading them more or see if NJB do a higher rated spring.