The 1.93" mount height was pretty much designed to get a Schmidt & Bender Short Dot or similar optic up over an AN/PEQ-2.

The 1.93" mount height ended up early on with the name "NV height" because it cleared most MFALs out of the FOV of an RDS or a LPVO, but it was not necessarily designed with passive shooting in mind, and was originally used primarily with LPVO-style optics.

Around the same time, the 5/8" riser was used to push the Bushnell Holosight/EOTech 550/551 up to about 2.1", among other things, for use with gas masks, which was also found to be useful for passive aiming.

The .410" riser was developed for use with the HK416, which has a taller top rail than the M4A1, to provide roughly the same height over bore as the 5/8" riser using the EOTech XPS.

The 2.33" height was developed by putting a lower-1/3 height Aimpoint T1 on top of a 5/8" riser.

The 2.26" height was developed in order to allow the Flip-to-Center mount configuration.

The 2.04" height was developed to line up with CNVDs mounted on common 1/2" risers.

Body mechanics will vary between individuals so the ideal height for passive aiming will vary as well. If at all possible, I recommend getting a couple different configurations to try out is worthwhile, and ironically where some cheaper accessories can actual be of some use, as you can get cheap 1/2" and 3/4" risers on Amazon just to try out different mount heights to see roughly where your "sweet spot" might be. As you can see above, there's not necessarily a "right" agreed upon answer across the board.

Because of some of the geometry involved, small differences in height can end up having a much larger effect than you might expect. At the same time, for the most part, most people can tend to generally use anything over 2" universally for passive aiming interchangeably. Some have more difficulty at 1.93" or below.

~Augee

Sometimes the guys with the most experience are the hardest minds to change--I'll put it this way, I would bet that at every echelon of comparable professional experience, you'll find guys who disagree that are using taller mounts.  

In terms of the legality aspect... yeah, again, I'm not necessarily seeing any difference legally between an IR laser or passive aiming, at least not in isolation, though if their perspective is that it's an ambush tactic, then I understand what they're trying to say, but that's an entirely different conversation.

Again, while it's not "new," passive aiming has become much more popular now than it used to be and people have become more conscious of it and factor it much more into their decision making when it comes to equipment and gear, and to some extent it's almost a chicken or egg thing.

Arguably, the more people get into night vision, the more important passive aiming gets, which is introducing more and more people to the concept of passive aiming and more people start talking about night vision capabilities and needing passive aiming capabilities, which leads more people to consider whether they need to consider their own night vision capabilities, and so on and so forth.

That being said, the "IR laser as primary" still runs deep with some people, especially if they've spent a lot of time doing it and have had a lot of success with it, and again, arguably if most of their success using it has been against asymmetric threats with far more primitive technological capabilities. However as the world and times shift, the threats are becoming more sophisticated as well. As the saying goes: "we've killed all the dumb ones already."

Now, one thing I will point out:

Passive aiming isn't the only reason for taller mounts, it is one of several--if you look at my post above I dialed down some of the ways that different heights came about, it's not all 100% about night vision.

I know guys who don't like tall mounts, but you point out they used to run 2" tall sights back in the day, and they'll say "well, we used to do a lot of training in gas masks." And it's kinda like... well, there ya go. Might they think you're stupid for wanting your rifle to be set up for gas masks when your command is not forcing you train in gas masks? Sure, but that's a decision you've got to make based on either what your threats are, or what threats you're preparing for, even if it's just hypothetical. Especially these days, a lot of guys are talking a lot more about wearing and training with gas masks than they used to (we've talked about it for quite some time).

Tall mounts are the same way. Do they come with a price? Namely comfort in the prone? Absolutely.

What are your needs and/or what do you want to accomplish/be prepared for? Is it something that's worthwhile to you? Like anything else, it's a cost/benefit analysis. How badly do you need to aim passively, and what penalty do you incur?

As far as things you can do to remedy if you're uncomfortable in the prone?

Maybe a slightly shorter mount? If 2.26" is too much, try something around 2" (absolute cowitness + 1/2 riser) or 1.93"?

Maybe a cheek riser/pad?

Maybe even extending your stock depending on how you run it--angles and geometry matter.

~Augee