All top tube lengths are not created the same. A top tube length of 550mm at a seat tube angle of 73 degrees is not the same as a top tube length of 550mm at 74 degrees. Totally different to the point that the number doesn't mean anything.

The fitting program that gave a saddle setback distance makes the most sense, except that the leg measurements need to be VERY accurate to get a good answer. Failing that the quoted seat tube angle is next best, except I can't see how they calculated this angle. The size my bike fit calculator made the least sense simply because it didn't use enough data.

For your purposed go with a bike that places the weight on the saddle and a little on the pedals. Avoid a bike that places too much weight on your hands/arms/shoulders. On a specification sheet you are looking for a more relaxed (smaller number) seat tube angle. Seat tube angles will be in a tight range from 72 to 75 degrees.

Ride some bikes. Take note of how balanced you feel on the bike.

Anthony