X-ray feeders per 517.73 (A)(2)

[Do You Like Ham]

How is this to be applied in the case there is a feeder to a panel (blue in image below), that then has a branch circuit (green in image below)to a single x-ray unit. The feeder article indicates 'two or more'... 'not less than 50%....'. But, leaves opaque what happens if a single unit.

Is one to interpret that since 51.7.73(A)(1) states 50 of momentary or 100% of long-time (whichever greater), that for the feeder a similar comparison must be made between the momentary vs. long-time current for the feeder (blue)?

 

[Do You Like Ham]

Follow on question to this... 660.6 has similar terminology regarding momentary, but the feeder is 100% of the largest two.. the branch circuit is still 50%.

Strikes me odd that a main panel feeding two sub panels, each with one such unit would have greater capacity than the sum of the individual branch circuits? Can any explain this?