I don't see an exception to the "within 6ft of the edge of a sink" for receps not readily accessible. I believe GFCI protection is required for a recep within 6ft of the sink even if it is behind the refer.
A lot depends on the way this Code section is interpreted. If you're working on new construction, most all of the kitchens I've seen have a dedicated space or enclosure slot allocated for the refer. 2017 NEC 210.8A states :
210.8 Ground-Fault Circuit-Interrupter Protection for Personnel. Ground-fault circuit-interrupter protection for personnel
shall be provided as required in 210.8(A) through (E). The ground-fault circuit interrupter
shall be installed in a readily accessible location.
(6) Kitchens — where the receptacles are installed to serve the countertop surfaces
(7) Sinks — where receptacles are installed within 1.8 m (6 ft) from the top inside edge of the bowl of the sink
IMHO, if the refer is inside its own enclosure or slot AND the receptacle is behind the unit it doesn't have to be GFCI protected irrespective of whether it's 6' from the sink or not.
Think about this for a moment - What if you have a Sub-Zero refer and the receptacle for that is up in the right hand corner at the rear of the unit. From my experience I've usually wired these units on their own circuit. Would you locate a GFCI receptacle behind the refer ? In order to get to that receptacle you would have to pull off the front of the condenser section to reset it. Would you use a GFCI breaker where the HO would have to go into the garage of basement to reset it in the event it trips ?
IMHO, I don't interpret the Code that way and I would NEVER put a refer on a GFCI protected circuit in a residence.
I'm sure the CMP's have all good intentions when they write these Codes but it's obvious they've never lost a refer or freezer full of food because a GFCI tripped.