Just realized I was loading my 6 inch vise off center for two years

I was surfacing a 12 inch aluminum plate on the Bridgeport and kept getting a taper across the face, like 0.008 over the length. I checked the spindle, trammed the head twice, and was about to blame the machine when I noticed the vise jaws were clamping one side of the plate way harder than the other. Turns out I had been setting the plate flush with the fixed jaw but hanging the back end way past the vise body, so it was twisting every time I cranked down. Pushed the plate in so both jaws grabbed even, re-clamped, and the taper dropped to under 0.001 on the first pass. Has anyone else chased a taper bug and found it was just how you were seating the part?