I mostly sit, which started when I tore my left hamstring in a Missouri enduro back in 2000. When I hit a bump, I let the bump raise my butt and then just straighten my legs underneath it.
I'm 6' tall and weigh 210#. (But, I think "tall". :^)
I use the Guts Racing tall/medium density foam. The medium density foam keeps me from sinking down into the seat foam, but the tall foam makes the seat feel soft. I've been running this combination ever since I first got Guts to make the GasGas foam and covers back in 2001. I sent them a stock seat foam for the two stroke and another for the four stroke (which accommodated the battery in the air box), and told them I wanted replacement foams in the stock profile and another taller seat foam which would eliminate any dip and make a "straight line from the rear fender to the tank".
It usually takes at least three years of me riding sitting down before the foam "sacks" and loses it's shape. Then, it usually develops a dent up at the tank and another right in front of the rear fender.
Having said all that, I sort of like that 10" wide GasGas seat by Fisher. But, until I get ready to drop all that money on a Fisher, I'll keep using what I've got and like, and plenty of Anti-MonkeyButt Powder. That stuff is the shitz.
Good Riding to All Ya'll!
Jim