trial and error, location-location-location and lastly shape of the sway bar.
Keep in mind that a sway bar is not going to stop or really even reduce the roll unless it is HUGE and I mean HUGE like huge enough to pick the other wheel off the ground huge.
There is always going to be roll, consider going diagonal up a slopped driveway from a flat street.
sounds like you have a tire width / offset / need tubs issue not an anti-roll issue
Just my 2 cents and with inflation, taxes and old age its only worth about a nickle!