The Kohler Class six rinses better then the Kohler class five.Without that info we don't know if we are comparing apples to apples.
But it's still lacking compared to other brands.
Since you are an engineer, I will put it this way.
The Class five left out all of the rinse holes at the back of the bowl.
Kohler's comment, was that the homeowner could "wax" the back of the bowl.
The Class six now has rinse holes 360 degrees around the bowl, but they are spaced so wide, that the water streams don't cover the entire bowl, they are thin water streaks running down the bowl with gaps in between.
This isn't rocket science.
Most toilet bowls rinse with water. Water cleans.
If the water doesn't touch the bowl, it doesn't clean.
The trapway on the five and the six has a sharp bend where it leaves the bowl.
Most plugs are there.
You will notice that the TOTO trapyway points the waste down the drain.
The Kohler trapway doesn't.