I have a pair of Dexter SST6 LE and they are great shoes.  Worked great at Nationals with the 8 sole and red leather heel (most slide combination)

However, I am having a tough time breaking in the H5 blue horseshoe heel (standard brake) It seems the inside edge of the horsehoe is not flat - there is a ridge that provides more brake. At the end of a bowling session, the inside edge has a black line of dirt on it.   The old flat sole of my SST 5's for standard brake broke in fairly quickly, but these horseshoe heels just can't seem to get there.  

Any body else had this problem?

SST'5s were a flatter design in the layout of the sole. If you look the SST'6s they are a bit more proped up in the air and having the progressive thickening heel like the horseshoes it tend to bite a bit harder to the lane upon pressure. You can do two things.
1) Sand down the inside edge which is dragging and slowing down your slide. Start coarse with like a medium grade metal file and work to a finer grit.

2) Try the standard old flatter heels. They fit fine as replacement heels as they are all one size, (very large) then just cut them down to size or let overhang. (Band saw and file work fine for trimming). If you have any problems or questions feel free to message me.