WAF is subjective...
That being said... the best placement in your 'space' can only be determined , IMO, is by utilizing the 'sub crawl'. Short of using measuring equipent, is to actually put the sub in the main listening position, yes.. in the seat... and actually crawling around on the floor, with your ears at the level your sub would be located, while playing bass heavy music you're familiar with, and wherever your ears tell you it sounds best, is the best location to place the sub. It really works.
And yes, pile it on... just say it's the 'best i can do, with what i have to work with' ... and then say that the next step up is "A Jericho Horn"
driver complement 6 X 18" woofers, 24 X 5" mids, 12 X 1" compression drivers
, $25000+ " and this is the best next option... and she'll cave... "look honey, I want the best available, within reason, just to make sure I do it right once.."
It worked for me... I'm gonna go Danley's next anyway, but it bought me some time....