I've probably missed something here, but what is wrong with starting down from 1900' at the KFA (ok 0.3nm before) with -3 degrees FPA. This will be 5.5nm to the threshold. So you have to lose 1900-55(elev) - 50 (over the thr) ie about 1800' in 5.5nm so you will need a little more than the 3.05 degrees suggested by the plate (327 ft/mile so try -3.3?).
mcdhu