Your room dimensions are almost exactly what mine are - 20X14 with an 82 inch ceiling. I haven't moved into my place yet, but I've already looked at tons of stuff, from getting crazy looks from my wife when I tell her I want to dig down, to just working with my existing space. You'll get hundreds of different opinions here, none of them bad, all of them interesting. Basically, you can make yourself feel good because there is always someone in a similar (or worse) situation, or you can feel lousy because there's a bunch of folks here who have better rooms than your local multiplex. I've been encouraged because even if I decide to use my existing space, without lowering the floor or raising the ceiling, it can be done really well. This room has an 80" ceiling, and is similar in length and width to ours:
First, check out this site for how far you should be from your screen:
The way I look at it, a 92" diagonal screen with 3" borders means that at 11 feet from the screen, I'm right around the optimal point per THX standards.
Then look at this link, which comes off the room riser "sticky" at the top of the Home Theater Builder forum:
According to this, with a front row 11 feet away, and a back row 14.5 feet away (the 3.5 feet between rows is right where Berkeline recommends for much of their seating), I need my riser to be only 8 1/2" high for the second row to comfortably see the screen. I could even make it lower if the seating I use for the front row is lower, which it will be. My couch is about 7.5 feet wide and seats three men or two couples comfortably, and sits lower to the ground than most Berkeline recliners. Now, even standing on the riser, a 6 foot tall person still has 1 1/2" of clearance. A 6'2" person would have to duck when getting into or out of their seats, but if you're 6'2" or taller you're probably used to ducking.
Plus, with the back of the riser about 15-16 feet into the room, I've got a few feet of clearance from the back wall, so that even folks in the second row are in a good position for 7.1 sound. These dimensions have an added benefit - the front row is about equidistant from the four corners of the room - ideal for SACD/DVD Audio listening. I'll use standard monopoles for the surrounds when listening to music, with the ability to switch to my quadpole Axiom QS-8's for movies.
Would I like another foot or two in height? Sure, and I still plan on looking at how I could even get a few more inches with some less complicated adjustments. But the fact is, most folks are dealing with rooms they inherited and don't crap $100 bills to pour into remodeling an already usable room, so you've got to play the hand you're dealt.
Hope this helped you as much as it helped me