What you need to do is get rid of the ratchet. Go to a heli-style no click throttle.

If you also need to fix the throttle stick does nothing during the last quarter problem,
expo is good. But you said "apart from expo" so I assume you're not using a computer radio.
This means you need to create expo mechanically.

You do this by setting up the arm on your servo so it's pointing almost directly away (or toward)
the carb at idle, and such that it's just a little past square with the carb at full throttle.

This makes it so that at low throttle settings the throttle stick doesn't do much (moves the carb
very little) and at high throttle settings the carb moves much more for a given stick movement.