Depending on which way you look at it, either their ankle 'recess' is too severe or they have too much padding around the achilles. The result is there is constantly too much pressure on my achilles. Comparing the back inside wall to yonex, the yonex shb101 is noticeably flatter.
I was using gel blade 3. the cut out aread should be for better fit. Obviously if the shoe back is perfectly straight then there will be a gap. Apparently the gel blade III recess is too big for me!