My stem choice came down to me wanting a more upright posture than I have on my drop bar bikes. The bike I posted has a top tube length that is the same as some of my drop bar bikes. One step I took was to mock up the flat bars with a stem reach length that I would choose for drops. This had me a bit more stretched out/leaned forward than I wanted for this bike. The forward reach on that riser stem is 6.5cm, whereas I might choose an 8.5 or 9 for drops. The rise also helps as the frame is on the short side, and I can get the contact points where I like them.