I had the same issue with my 3913TSW. Yet I'm very capable with a 6904/06.

Clearly it must have something to do with the grip. My theory is that I just wasn't able lock the 3913 down under recoil, and the shots would "slip" away from POA. I feel like the wider grip on the 69XX guns lets me exert a lot more lateral force with my support hand... which helps to stabilize the gun. I find I get the same advantage with my Beretta 92 Compact. And I shoot both of those platforms very well.

For single stack DA/SA carry, I went with the Sig P239. While it's not quite as svelte as the 3913, I find it outrageously accurate in my hands. Strangely, its grip is nearly as thin as that of the 3913... yet for some reason, I get a better purchase with my support hand. And the addition of Karl Nill grips or Hogue G10s improve that even more. Also, I think the heavier slide on the P239 might keep it a little more stable while shooting. Caveat: these are all theories, based on "educated conjecture"--not science.

At the end of the day, I have to conclude not every pistol is going to work for every shooter. The 3913 is a great gun, just didn't suit me quite as well as others.

Though I still often think about buying it back from the friend I sold it to...