Bike "size" is so variable that its difficult to compare 2 bikes. They may differ in the bottom bracket height, and the point on the seat-tube where you measure. For any size bike, the top tube length may differ.
My LBS sized me by eye, ordered the frame, and let me play around with stems and bars for a few weeks before wrapping the bars. There was no systematic "fitting" process, but I ended up with a bike that fits.