Many thanks to all who replied.
Reports of leakage and migration all seem to have qualifiers. "It only leaks or migrates if..." So overall, there is great success with these cups with little of each.
Using a very unscientific hash-mark system:
Diva = 21 replies
UK Mooncup = 13 replies
Lunette = 7 replies
10 replies like to ride low
21 replies like to ride high
10 replies like to ride on or follow the cervix.
Because "high" and "cervix" outnumber the "lows" 3 to 1, our cups and bodies defy the instructions to "ride low."