I have never assembled it in this configuration, but looking at the drawings of the cases I would probably choose a power supply with straight cable outlets. The advantage of the shift variants is that the cables are pulled out from behind the side panel. Mounted upright, the 20+4 pole or the CPU cable could possibly be too short as they are often not excessively long.
Yes, I have the H9 Elite, which is the same case as the Flow,but with glass top instead of the perforated or metal mesh on the H9 Flow. It work for me as the connections all sit on the top and the fan is directed through the side mesh panel.