Yep, that's exactly what I normally do to determine offset. Just this one time my images were coming out poorly until I realized that the KStars offset is only 8, and thus my calibration library needs to be re-shot. I also run all my sensors though SharpCap's sensor analysis, which I occasionally use with the Smart Histogram feature to suggest good exposure lengths when I change cameras or have different sky quality. Great feature, but I don't think it recommends an offset so that's always a separate step. BTW, SharpCap uses the term "brightness" for offset.