Most of my comments have been about main speaker levels (mains, center, surrounds).
I believe sub leveling is a whole 'nother can 'o worms...

The rat shack meter is progressivly inaccurate between 2-20db from ~80-ishHz down to ~10Hz (and worse down to 0).

I'm guessing no one here corrects for these faulty readings by doing some very detailed math, since the test tones you guage by are an equal output of all these tones at the same time, but then again... maybe they're not?
Are you sure what exactly the chosen test tone is outputting? Some of you may not be.

Then factor in room modes that change the bass level throughout the room beyond the tiny point you SPL metered at.

Then play a CD with weak bass and want to up the level. Then put on the DD intro on Phantom Menace and bottom out your sub.

'Real world' it just works/sounds better to guage by ear by knowing you system inside and out.

How many use wall 8' bass traps in the corners of the room to cut these standing waves? I do, and my bass is tighter and more accurate than it was previously.
How many have thought about how the distance from mains to the sub effects it's phase accuracy?

Now tell me you have have that sub set perfectly, or more prefectly than mine is.
At least think about it before you disregard my comments as being 'not what most people do'.

Most people use TV speakers. Or do you mean most 'HT users'?

Most of them use Bose. Or do you mean 'HT forum posters' like here?

Most of them use SPL meters in assorted methods that all (or 'all but one') must be at least somewhat inaccurate.
They judge with thier ears that this is more accurate than when they judge with thier ears. Odd ain't it?

The people with the most advanced knowledge and radical thinking about hi-fi are by far in the minority.
Note- I don't claim to be one of them, but just possibly more-so than some who assume the majority is typically correct just 'cuz they're the 'majority'.