Pears vs. "T"s
Sounds kinda like the transition from the nose to the wide part of your saddle may be too gradual. More like a pear than like a capital "T". (as you look at it from above)
If the transition is too gradual for your particular build the crease/pantyline/fold will rub as will the inner rear part of your thigh.
I know that I need a pretty abrupt transition, which I've gotten with my Terry Sport and my Brooks B67. My women's Serfas Niva is overall a nice saddle, but not abrupt enough for my body. (it's more pear shaped)
Once I switched from my Serfas to my Brooks my chafing issues cleared up.
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