Being a boot fitter....
You need to strap using the powerstrap first. But, do not put it on the outside fo the boot....put it under the plastic so that it only holds the liner. The point of the powerstrap is to hold the top of the boot to your let....the line is what is important because a space there will cause shin bang. So, after the powerstrap is done up around the liner only, strap the top buckle, and move down, only buckling on the first place possible. Once all buckles are fastened, then start back up at the top and tighten one at a time. If you jump up to real tight, it can easily cause cramps and push your foot to funny positions in the boot. The top buckles are the important ones as they are the ones that hold your foot back and the bottom buckles should just be a thumbs tightness. If you can't buckle the bottom buckles with your thumb, they are too tight.
That is my 2 cents as a boot fitter.