Replying to Full Tilt Vs. Dalbello Vs. Every Other Ski Boot

I got the 2017 Edollo boot in a 27.5, earlier this season I was rocking this years dropkick but I got new skis and they were mounted for 27.5 so me and my buddy traded and I liked the smaller boot. 28.5 was hard for me to butter and on the 27.5 was easier, now I fit in the boot just fine and I find myself having to buckle my boot as much as I can to really butter and my heel still feels like its popping out. I have a very wide and flat foot but is it because of the #6 flex tongue or something else? I've been looking at other boots such as Dalbello, Nordica ETC.. What will help me fix this?