The power of the in position 3 bet + a river bluff

Full Tilt Poker $0.25/$0.50 No Limit Hold'em - 9 players - http://www.thehandconverter.com/hands/329805
The Official DeucesCracked.com Hand History Converter

MP1: $11.15
Hero (MP2): $62.00
CO: $11.05
BTN: $21.00
SB: $44.90
BB: $9.35
UTG: $57.40
UTG+1: $32.90
UTG+2: $40.85

Pre Flop: ($0.75) Hero is MP2 with Qd Ac
2 folds, UTG+2 raises to $1.50, 1 fold, Hero raises to $4.25, 4 folds, UTG+2 calls $2.75
When you 3 bet (UTG+2 had a PFR of >13), your opponent generally puts you on a pretty narrow range. Things going in my favor include the fact that PT3 build 4 does not include (by default) 3 bet %. Therefore, people at $50NL, as a general rule, are not looking at 3 bet %. Therefore, to them, 3 bets mean one of 3-4 things: AA, KK, AK and less likely QQ. If you widen that range, you can get away with a lot more. Therefore, I 3 bet this "wide" raiser with AQo

Flop: ($9.25) 6s 4c Ks (2 players)
UTG+2 checks, Hero bets $5, UTG+2 calls $5
I can represent AK on this board, but I'm not happy at all about his flat.

Turn: ($19.25) Js (2 players)
UTG+2 checks, Hero checks
Spade draw gets there, and I'm giving up on the hand.

River: ($19.25) 8s (2 players)
UTG+2 checks, Hero bets $9, UTG+2 folds
A 4 flush is out on the board. Is UTG+2 ever going to check to me in this spot with the As or even Qs (second nuts)? I can easily represent AKo, cracked by the turned spade, but backdoored to the As. I'm fairly certain that he does not hold a spade either. As far as bet sizing is concerned, I waffled back and forth between $14 and $10, before settling on $9. I wanted to make the bet significant, but not so much as it looks like an outright steal. I wanted to make it too much for him to call with no spades or a small spade. However, I did not want to put a huge percentage of my stack on the line in the event I get called or check / raised. Therefore, I felt like $9 is a "call me" bet, but a significant (for these stakes) bet where he can't call me without a good spade.

I think my story makes sense, too - because I 3 bet him strong pre flop and led the flop on a King high board.

Final Pot: $19.25
Hero wins $18.30
(Rake: $0.95)