Untwisted the pressure is on two points either side of the rod, twisted over once it only acts on a single point covering less area of the rod the pressure on the single point the pressure dissipates in the foam. Untwisted it could be compared to a bar of steel exerting pressure from a hand on each side pushing the bar into the foam leaving a pronounced dent in the foam the bar being the rod to take it to extremes this could snap the rod, twisting the strap once puts the pressure on the whole length of the foam with the foam dissipating the energy exerted on the single point of the rod and spread from one end of the foam to the other. If you can see what I mean, maybe I have made it more confusing .
I didn't like Wheatley rod rests which were tapered from the centre towards the ends putting a lot of pressure on the rod itself without any dissipation of pressure.
There needs to be some marking, no marking there is no dissipation of the pressure, but marking is minimal with the strap twisted as it has more area to dissipate pressure exerted on the rod itself. Adding neoprene lifts the rod allowing more pressure to be exerted on the rod itself, giving more need of a single twist to the strap.