Wow! You are describing my life a few months ago perfectly! My son also did this (he sleeps in a toddler bed though, but smashed the poop all over the room). We had the hardest time getting him to go poop on the potty. The pee was a piece of cake, but we just couldn't get him to poop on the potty. The best advice someone gave me was from a behaviorist and friend who said that the muscle movements and what is required to make a BM are different and that he'd have to experience making a BM on the potty at least 3 times before he is able to understand what he has to do when he has those urges and poop where he's supposed to. Also, my son was very curious about his poop and (gross, I know) loved to play in it. We spent MANY MANY clean-up sessions talking about how poo-poo is yucky to play in and can make you sick. One thing that worked was letting him watch while my husband had a BM. Daddy talked to him about what he was doing and they both listened for "plops" and giggled when they heard them. I know it sounds gross, but it worked, because he loves to make "plops" even today!