Final glide

I use an arrival height reserve. When flying to a destination airfield I readily and easily make mental adjustments up and down from it depending on conditions and distance to go. For me the benefit of setting the arrival height reserve is that if I see a green blob on my moving map when I am away from base I know that I have a fighting chance of reaching an alternate airfield. If you use a zero reserve then a green blob on the moving map is meaningless and you have to read the arrival height beside it.

By the way, at startup (after the gps has acquired) I check to see that the arrival height at the airfield I am sitting on is approximately minus my arrival height reserve. If the OP does this it might help him diagnose his problem. OP, please do report back to us on any further findings.