I'm using the Retronic adapter and regular Atari 2600 paddles. I can see in windows, the control panel calibration, with Raw Data checked, that throughout the entire range you can turn the paddle that it does read values from 0 thorough 255 with 128 being the center. The movement is smooth also. But in Stella, it only uses a small portion of that range and it's a bit laggy even with the sensitivity turned down to 1. So it's hard to control and when your at the edge of the screen it feels like it gets stuck there briefly. My mouse works better. I tried the Z26 emulator, which feels a little better but still not good enough.
Hopefully when the Stella authors work on paddle emulation again, they will provide more settings to adjust things and improve control overall.