Either you have too much Droop (I run max. 6mm on Blocks when using Sorex Tires) or your Dampers might be too short.
Make sure, that the Downstop screw doesn't limit the rideheight.
You could also check your suspension blocks and shafts if they are flat/straight.
But normaly, if I couldn't make rideheight, it were the Downstop screws.