Neville,

If you are using a computer radio, adjust the elevator travel to where it won't snap, and use that as a low rate. It doesn't take very much travel for these planes. I only have about 15mm of travel in my Edge, for a low rate.
As JrWilliams said, for harriers you have to find the right AOA. This will take full elevator travel, high AOA (45 degrees or more), careful throttle management, and using the rudder to keep it straight. When you transition into the harrier, you will get some wing rock, so get the nose high quickly, and use small aileron movements to counter.

Keep at it, you'll get it!

Bill