Not at all. Based on Apple's definition of "retina", it's essentially the distance at which the size of a pixel drops below the resolution threshold of someone with 20/20 vision (i.e., 1 arcmin of angular size). 1 arcmin is 0.01667 degrees, give or take.
So if you know the size of a pixel (and if you have the ppi figure, you do, as it's simply 1/ppi), you can solve for distance, which is explained better than I can type out formulas on the forum by
Wikipedia.
220 ppi, for example, puts pixel size at 0.00455", and solving for
d gets you 15.71" or so.
You can also plug the numbers into a calculator if you don't want to do the math yourself:
http://www.1728.org/angsize.htm
That sets the "retina" distance (I rounded to the nearest inch). However, because people tend to sit further away from larger screens as a matter of personal comfort, you have to factor that in as well.