"Comfort" is all relative....
I wouldn't say that the factory did a very good job setting up the seat rails or heights, and with a fixed-back seat you're more likely to be uncomfortable, than comfortable.
I'm only 5'9" and I'm amazed at how little adjustment there is in the factory seat slides. I set the seat in the rearmost position to get the pedals a normal distance away and to get a slight bend in my arms on the steering wheel. I can't imagine how someone 6' or taller gets in there without feeling like they're in a coach-class airline seat!
My plan is to modify the stock seatrails so that I can move the seat back all the way to the "step" in the rear floor... then play around with the rake of the seat and the height to give me decent sightlines out the windshield and head clearance around the rollcage. Once that's all established, I'll cut,weld and modify the stock frames until they put the seat where I want it. Then I'll modify the passenger seat mounts to match the driver's side visually.
Seat rails are cheap....I'd just do what makes you comfortable in there and worry less about what "factory" was. IMHO
-G