I can see how this is a problem for many. Driving, much like any activity, is dependent on preference and personal techniques, so tuning the specs can be very subjective...Anything that can gets the job done safely is good. That floating frame of reference is indeed difficult to get used to, but not impossible if you take a different perspective and put absolute trust in your intstruments.
If you point the mirrors out towards your blind spot until the body of your vehicle is JUST out of sight of the mirror, your frame of reference is a very real, very defined space--anything beyond the edge of that mirror is your car.
Now that you can't see your own vehicle, you naturally feel like you are flying blind. Thats ok. Pilots are trained to trust their instruments. Firefighters are trained to trust their suits and respirators will hold up in the heat. Without that trust, they'd be too scared or uninformed to do the right thing that saves lives in crisis. The same mindset could be applied to your trust in the mirrors, as those objects will always bend and reflect light the exact same way.
If your driving style is very "seat of the pants" or driven by feel, this technique is virtually worthless. Likewise if you share a vehicle with someone, or find yourself slouching or shifting your body position often while driving. tl;dr--Try it out if you are inclined to be a regimented driver or tend to treat yourself as an extension of the driving tool.