what is your goal exactly? Want to collect multiple varieties? Want good fruit production for the smal? space you have available?
Generally i would be careful adopting commercial spacings in a backyard grower setting.
Those who have commercial orchards usually also do more night frost protection, and thus are less likely to have a year where the tree produces little fruits and grows like crazy, way more than the allotted space.
And even if they do run into those issue’s they can usually root prune with tractors fixed blades and stuff. As a hobbyist that’s usually not an option.
Planting so close will give you some shading. and that could lead to increased disease pressure and usually reduced fruit productivity.
I would plant at more “normal” spacings and do multiple varieties per tree. Or look into espaliering some tree’s.
you could play around with
http://shadowcalculator.eu/
to see how much and at what times (of day and of year) they shade each other.
if explained more about that tool in this topic.
i would also worry about having the horizontals of the UFO so close to the soil. I have no scientific proof for this. But i think 6 inches off the soil is to close. Will likely lead to higher disease pressure. (the branches stay moist longer. Especially if weeds grow. Might get damaged more often when weeding etc