You need to have a path for the actually moving air to get into the room other than by vibrating the screen.

Three examples:

1.RPTV placed in front of a fireplace because that, too, was the only place for it. There was a brick hearth* about ten inches high and the TV went on that. We had no place for the sub so we got the bright and hilarious idea of putting it behind the TV, actually in the fire area.

Worked great until we got to the side of the TV and saw that the screen was moving forward and backward with a total excursion of about an inch, maybe more. We had to put the sub in the room.

2.Overseas client's brother's place: We turned a theater with about a 12 ft 4:3 screen into a theater with a 20 ft 16:9 screen. The screen was surrounded by drapes with no real open ventilation. It was a rear projection setup. Four 18" JBL subs are in the corners of the space behind the screen (and another two in the room), which is about 400 sq ft and 15 ft high, so maybe 6000 cu ft.

Upon playing the cut from "The Art of Flight" with the gnarly bass, LOUDLY, we observed the screen moving back and forth with a total excursion of almost two inches. We improved this by careful EQ of the major resonances. Bass is still visible moving the screen when you're off to the side of it.

3.Overseas client's system: Much larger screen, about 30 ft wide 2.35 with movable masks. Same 4 JBL subs behind the screen (and another four of them in the room). The space behind the screen is about 12 x 50, with a height of about 25 ft, so a volume of about 15,000 cu ft.

Upon playing the cut from "The Art of Flight" with the gnarly bass, LOUDLY, the screen hardly moved. By "loudly" I mean that the client's engineering staff measured a power draw of about 18 kVA while playing that. The projector is a Digital Projection Lightning, so the power draw was not nearly all just audio.

Anyway, in the last case there's a huge amount of volume and a very large surface area, both of which reduce the amount of energy that will move the screen.