That Mark's rack is a Rivendell design, it makes sense that it works well with bars that are set up higher than traditional road bike bars. Perhaps the M18 would have been the better choice but I wanted maximum versatility and the geometry looks in pictures to be similar.
The struts are not a problem. When I get the bag in the right place, the struts that came with it and the 420s that I got extra to go with it, will stabilize it well enough. Although, just playing around, there is not much difference with two vs. four bars so no worries there.