I feel at the walk you need a LOT more leg. He needs to be marching, which will help with his deep headset (which is evasion)
Also your stirrup leather could probably go down a hole as your knee is sticking up over your saddle and shoving your entire leg forward as a result.
The entire ride would be lovelier with more leg into your hand. He's very heavy on his forehand and too deep with his contact as a result of evading. Get him to stretch, which includes not sitting his trot until he's really stretching out.
Only once you can get him stretchy can you bring him "together" and start to really work his hind end properly, instead of just his front end.
"Strength is the ability to use a muscle without tension"