You can set expo in either the transmitter or the GCS. That makes the center part of the stick less sensitive. That will surely make it feel better.
Last I heard, RTB alt offset is measured from the min of base altitude and current altitude. If you climb a mountain, it will immediately climb the offset (e.g. 4m) and stay high until over base. If you descend into a valley it will climb straight up to base + offset before moving horizontally.