OK some more data for you.
Yes, the entire layout is starting to scream for DCC, but I am a cheap, stubborn, railroad tycoon.
I corrected a duplicate block number in earlier pic. The short curve is a seperate block where a short loco could park.
I'm thinking a train comes round the mountain clockwise to end of Block 10.
A second loco will make it's way in reverse to couple onto train to help over the summit. This would couple up with couplers over a gap in the rail between two blocks. Normal DC operation I've done many times.
But now reversing the process (with some imagination) , the train comes round the mountain downhill clockwise to end of Block 10 and has to stop and uncouple the lead locomotive so it can go back to the yard facilities (roundhouse).
Looks like I answered my own question the two locos must be in separate blocks during uncouple, so the gap needs to be right over the uncoupling ramp.