Just a suggestion... The HL-20 is VERY sensitive to minute deflections in the wings to make it go from glide to spiral plumet... When it was being developed I made about 25 different models with the given dimensions (the aesthetics had already been determined). I could only change the wing angle and weight distribution. Basically each prototype had 1 degree changes of angle in the wing, until the final one actually had an amazing, almost flat, glide profile (with the usual corkscrew boost). This said, I am guessing that the best way to flight trim the thing would be with the use of trim tabs like I used to correct similar problems on my Fake Wulf kit. One on each wing would allow you to bend them up and down as needed to obtain a decent glide. If you want to PM me with your address, I'll send you a pair of the trim tabs for you to try out if needed.