Sealed Box for 12" Alpine Series S

I recently started this thread asking about how to build a vented box for some alpine drivers.

Some people recommended here and on Reddit that I go for a sealed box instead.

The manufacturer recommends a 0.85 ft³ box as the ideal of a recommended range of 0.5-1.5ft³

WinISD tells me F3 will be 45hz for those sizes, though at 20Hz, a 50L box will be around -14dB and a 35L box will be at -15.5dB. Qtc will be 0.772 for the small box and 0.709 for a 50L one.

50L is not much larger than the recommended 35, but it's a bit larger than the recommended maximum 1.5ft3 (42L). And it fits the mythical 0.707 Qtc

Is this a reasonable box for a HT system? I plan on having 2 of them in a small room. Considering room gain and 500W RMS to each, the total SPL at 20Hz should be 107dB at 20hz (115dB after 45Hz)
Yes that's what I suspect, these figures are usually for car audio use. And I wouldn't be surprised if they were undersized to claim "they use up little space".

One thing I noticed is that sensitivity in Type R is 2dB lower than type S. While in magnitude plots Type Rs come out 2dB ahead, in SPL plots, R and S perform basically the same.