I don't know if heavy lance thrust out reaches great lance couch. I think the angle of attack comes into play here...if you are both completely straight on (like a joust) I'm pretty sure the great lance couch is longer, but most heavy lance thrusters know how to put their horse in a position to get the best reach while keeping their horse as far away from harm as possible.
Thrusting with a polearm doesn't add any length to the reach, so that's why I think it's shenanigans. The only way this is possible is if you couch a lance it makes it shorter than the normal reach...that would be hard to test (at least with the normal melee reach tests).