My theory on that is in a side dressing type scenario, it’s harder to get a good seal (wheel tracks from planter, sprayer,etc) all the time with a three point mounted bar.

also even though a operator thinks they are getting a good seal, a certain percentage is still seeping out, let’s say it’s 2%.  2% of 235 is almost 2lbs over 150, which in itself doesn’t seem like much, but owing to the expansion of nh3 at 75° or so soil temp, and dumping it in the same sized slot as a 150lb rate i suspect it’s more than 2% loss at those high rates.

I think at those higher rates mole knives would be of great benefit, but didn’t have the time to try to see if they would make a difference.