IMO, stand over height should be one of the least important things for selection of a bike. Anyone riding a unloaded road bike for pleasure or exercise can simply lean the bike over when stopped. Which is what I did for most all my younger life when I rode bikes that were way oversize for me. Still to this day at stops, I'll stay in the saddle and just lean the bike with one foot on the ground.

As mentioned by several members, the smaller frame will have a lower frame stack. Which means the height of the bars will be lower than the next size up. And reach to the bars going to the next size up doesn't increase very much at all. And that can easily be made the same with a stem change.