A 20" feed line does sound to be a bit long. I can't imagine where your tank is for it to be that length on this plane.
My tank sat just behind the firewall on a slide in tray so the feed was very short. I've used a Super Tigre 2500 and a Super Tigre 3000 both running on glow in my Dynaflite Super Decathlon.
On all my gasolinge powered planes, I keep the feed as short as possible, even thoutgh they use pumper carbs. A pump will still not be suitable with a line which is too long. There are only two lines on the tanks - one is feed/fill with a T connection and the other is vent, wrapped over the tank in the standard fashion to prevent siphoning of fuel.
Could it be that you have a problem with your vent line, thereby creating a vacuum? You could try pumping all that you want in that case to no avail.
As for the pleasure of flying this plane and how it handles, why not wait until you try it and then you be the judge if it suits your likes as opposed to others' opinions on it?