are you using food as a lure? you may have to lure him closer to you and use his head and nose to position him properly. it took Heidi a while to get a good flip finish. she would always kick out to the side. by holding the food up a little higher ( so her head / nose is up) and the food closer to my side about chest level helped her. also no food for a improper finish ..

 

I don't know how you are teaching the flip finish. For Gunner I had him sit then moved in front of him and called for fus as I stepped directly into him (short leash to hlelp) which made him jump up and move to get out of my way. As he did this I took one step forward to bring him to correct fus position and he sat. After many practice over time he got it.

For Shrock I started much younger and used food as a lure. I sat him directly in front of me just like Gunner and stepped into him and as he moved out of the way lured him into position with the food as I took one step forward. Shrock got it faster but I started younger.

BTW mine do both finishes.

Hope this helps.