This could mean carrying a roll around as well as a seat bag and the rifle.
Think I could be getting a bit overloaded here.
I would like to suggest that a kneeler is where the shooter kneels in whatever position he is comfortable with, so long as the wrist is unsupported and the rear foot is near vertical. The seat bag position can be used in any way that makes the shooter comfortable; under the knee/under the knee and shin... whatever.
The big advantage to this is that its much easier to police.
Having tried this and the proposed way, there is little or no difference to the added difficulty of a kneeler shot. The proposed position is just a lot more uncomfortable (pain)