I'm not doubting your results. Heck, I would love to see the same result. I think I see the biggest difference though. With 8 padles on a 20" tire, you didn't have a second paddle in the sand for as long as you did when you went to the 10 paddles haulers. You would have been really pleased if you had gone to a 22" tire and dropped your front sprocket one tooth [or increased the rear two teeth] to make up the gearing difference. The taller profile keeps each paddle in the sand for longer than the 20". The larger radius also helps keep the tire on top of the sand, so there is less parasitic loss from rolling resistance and less "climbing" out of the holes a tire can dig.

As they say, "Size does matter" LOL