While I agree that you should contact a club, I also am looking at the web page for the "zoom pilot" which is the closest thing at hobbico's website.

What does those 20 feet look like? Are they smooth, then a drop? Is the plane climbing steeply, then dropping?

If it is the first, I would try is a little up elevator. Since they only provide two channels (throttle and rudder) you are limited to setting the elevator before takeoff.

If it is the second, I would center the elevator and then slightly rise it. You should barely see a change between the stabilizer and the elevator.

In fact, you want it to glide slightly downward when you don't have power, and climb when you do.