I'm really not sure what Dell (or whoever else is pushing this) is trying to accomplish. A standard 32" 4K monitor exceeds retina requirements at 2ft!
At 5 feet most folks won't be able to tell the difference between that 4K monitor and a 1080p panel the same size - and could save themselves a lot of money + GPU power by opting for the 1080p.
If 2ft from a 40" monitor is fine for your neck, again, glad it works for you. But ergonomics is about avoiding strain and injuries not the minimum your retina needs to distinguish letters on a screen.
The 2ft was in reference to the 32" monitor Dell's advice references. I sit roughly 3ft 6in away from the screen in my desk setup - which per a Television-oriented calculator is about optimal for a 40" panel.
I'm honestly not sure why PC-oriented calculators are so much more conservative about field-of-view than THX is.
Probably because with PCs you typically want to be able to focus on any particular part of the screen without moving your head a lot while with a tv relying on more peripheral vision is normal and expected.
At 5 feet most folks won't be able to tell the difference between that 4K monitor and a 1080p panel the same size - and could save themselves a lot of money + GPU power by opting for the 1080p.