Marty, it's a simple matter of geometry. As Mike pointed out in post 2, there is a calculator you can find in the dedicated theater design and construction subforum. The sight line for the second row is the critical design element for riser height, and it is determined by 1) the height of the heads of viewers in the front row, 2) the height of the lower edge of the screen, and the distances between those three elements (first row, second row, and screen). If you input the distances and heights of the screen and first row, and the distance of the second row, the calculator spits out the height you need.
Obviously, there will be some trade offs. If you thought your screen was going to be as tall as your wall, you'll be sad to see how high the second row needs to be situated to have an unobstructed view. Of course, you could just leave the view partially blocked, or you can move the screen higher. Alternatively, you could squeeze the rows closer together or find lower front row seats or taller second row seats - or even stagger the seats left to right to help mitigate the problems. It takes a few iterations to nail this down, and it's almost impossible without diagrams.
Okay, so this will sound harsh - but I'm going to say it anyway. You started by saying that you're finishing up your dedicated theater, but really - this should have been step 1. The first thing to do was to situate the MLP in the room, then design an audio solution around it, and fit a video solution to that. Then you go back and tweak. Expect a couple iterations before it's finalized. Do you have a bass system in mind? (probably already purchased, if I know you.
Let's take a stab at this, shall we? I'll put the MLP front and center. Two-channel aficionados and mixers have determined that bass is generally best (smoothest) at a position 38% back from the front wall or rear wall (Both Ethan Winer of Real Traps and Glenn Kuras of GIK Acoustics have articles about this on their websites, but it's still just a starting point). 17' is 204" and 38% of that is 77.5 inches. So that gives us two good starting points to consider. Measured from the screen end of the room (screen wall=0) 77.5" and 126.5"
Let's put the top of the heads in the front row at 78" back from the screen and 42" (a height chosen as typical in my experience) for a first consideration. From 78" back, a 110" screen is going to be large, but maybe not too large - so let's start with that. A 110" diagonal 16:9 screen is about 58" tall. It'd be nice to put the front row eyes about 1/3 the way up the screen, so that means 1/3 of the screen is lower than 40" (1/3 of 58" is about 19") So we can extend the screen 19" below the 40" elevated front row eyes to put the bottom of the screen about 21" above the floor. Like I said - this might be too big for a front row this close, but let's follow this through for now to see what it does to the second row and riser.
The second row will be at least several feet behind the front row. Experience has shown that for home theater recliners (lazyboy type or similar), you'll need 6.5' between row locations to allow people to move between the seats while they are reclined. So if we add 6.5' (78") to the viewing distance of the front row to get the viewing distance of the second row, we get 156" (13') for the second row. At this point, we have all the data required for the calculator to give us the riser height we need. http://calc.xn--f5a.net/
Rut roh... that's going to be a 27" riser. That's not going to work in your room with 8' ceilings. So what do we do? The easiest thing in your case will be to move the screen higher on the wall. You don't want to go too high, but some is tolerable. With the seating positions the way I've laid them out, for every inch the screen goes up, the riser can come down that same inch. So, to get your riser down to a manageable 12", the screen would need to go up 15" to be a total of 36" above the floor. That puts the top (58" tall screen, remember) at 94" - basically at the ceiling. That fits, but it's not good. (light reflecting off the screen will illuminate the ceiling and make for poor contrast on the screen, as well as be distracting).
So what else do you consider? If you move the front row back without moving the rear row, you improve the sight lines at the expense of clearance. You won't get more than a foot this way unless you use different seats. And moving front row back by one foot only brings the riser down from 27" to 22", so that's not really helping. You could move both rows back, but that's even less efficient at bringing the riser height down (though it may be needed anyway, to keep the front row from being to close).
Where's the happy medium? I don't know exactly, but you will have to try a few times. Good luck.