Upgrading from 2 subs (Front L/R) to 3 (Behind couch)?

[SPIDERone]

Currently using 2x Klipsch R-12SW subs in the front, and love the effect in movies. Looking into getting a 3rd (since it's on sale this weekend) to place behind the couch.

I definitely have enough power coming from the front 2 (located L/R next to the TV), the 3rd would be placed in the center behind the couch. Hoping this would help to "feel" the bass even more. Good idea? Bad idea?

Listening space is approximately 10x10 feet (7.2 setup) in the middle of a ~20x12 foot room. I was thinking of throwing it between the surround rear L/R chanells. The front subs are directly under the front L/R channels.

Good idea? bad idea? Overkill?

I don't need "more" bass, but would like to get some added 'feel' from one without going full-on with purchasing a buttkicker or similar setup