Sony Support's recommended viewing distance for 4K and 1080
Multiply the screen height (NOT the screen's diagonal!) by 1.5 for 4K. The height of a 55" 16:9 screen is 27". So, 27 x 1.5 = 40.5", which works out to a 3'-4.5" viewing distance with a 4K source, in order to be able to see 'FULL' 4k.
Multiply the screen height by 3.0 for 1080. So, 27 x 3 = 81", which works out to a 6'-9" viewing distance with a 1080 source. IMO, this distance increase is so you can't see the 1080 pixels - just a guess.
We have a 159" 16:9 screen which has a height of 78". So, for us, with a 4K source, we would need to sit 117" from the screen. Which works out to a 9'-9" viewing distance with a 4K source, in order to be able to see 'FULL' 4K.
We have sat 12' from our 159"screen for over 12 years. Even at 12' from the 159" screen, we can't see the pixels with 1080. Using Sony's recommended 3 times the screen height for 1080, we should be sitting 19'-6" from the screen for viewing a 1080 source !!! We are happy campers with the 12' distance with 1080 sources.
When we get a 4K setup this spring/summer, we will sit 5'-3" from an 85" 4K set, as per Sony's recommendation, so that we will see 'ALL' that 4K has to offer.
For those of you who sit at 6'-10' from a 50" to 85" set, viewing a 4K source, I respectfully suggest that you buy a good pair of binoculars (I recommend Zeiss 10X42's) and a good tripod.
And for those of you who sit at 10'+ from a 50" to 85" set, viewing a 4K source, I respectfully suggest that you buy a good 20X spotting scope with a good tripod. Again, I recommend Zeiss (I used this brand for many years hunting elk - back in the day).
For only then - for the very first time - you will TRULY see 'ALL' that 4K has to offer, due to your too long viewing distance. IMO; and Sony's too.