Are you talking a 120" screen diagonal, or width-wise here?
For that Vanderwyst layout imposed on your space, are you extending the room past the curtain bulkhead?
Do you know that a 10" riser is adequate? A side sightline diagram drawn to scale, is a really good tool, if you have
seating measurements. If the room could be extended, then why not center the space, and have the entry door up
front, on the side wall, in front of the scren wall? Here's That JBL room pciture I was hunting for, that shows the entry
door up front. Something like that would eliminate the off center design and let you potentially extend the room.
Seating on room boundaries is a very commonly made mistake. Put another way, it's simply asking too much of a space.
Most people want the extra seating, but I prefer value for my money. If one can get by with less seating, then that's
simply budget for another feature or two. (Proper room design starts with seat selection, and flows outwards from there.)
If I want extra (audio-compromised) seating, I'd simply drag in a couple of extra chairs.
If that riser is simply an option, I'd prefer the room drywalled down to the floor and add my own riser after the fact,
where I have control over size, height and shape.
I'd be worried about screen weave being visible at a 9' seating distance. Screen selection here would be very important.
Seating choice would also be important. Most people like their ht recliners. I find them simply too comfortable, to doze off in.
If your seating doesn't recline, two rows of seating is more compact deepth-wise. Might be a design tool, to keep seating off
the back wall.
Can you extend the room to deepen it? Would the Mrs be onboard with that to get her 2 rows of 3 seats?