I recall a story about a cab ride where the engine backed around a tight corner, and the writer had act quickly to avoid losing their thumb between the cab and the tender. Photos of 622 and her sisters confirm the tender should be startlingly close to the cab. However, it would be a bit of a disaster if the tender coupling were so short that the tender fouled the engine on Pembroke’s tightest curve.
That curve is 36″ in radius and you’ll find it at the entry to the roundhouse. So I whipped up a couple of test couplings to see how short they could be. I can’t come close to the real coupling length, but my model needn’t look like a toy! While I was at the south end of town, I also tested the couplings to ensure the engine will fit on the turntable, because, well that would be a bit distressing if it didn’t!
The shorter of two couplings just makes it around the corner. 
The longer of two couplings, and 622 still fits on the turntable.
Pembroke:87 
The short one is pretty close, but it works.
Yah, I might add a couple of scale inches just to be sure.
Always nice to see a project ‘out in the world’.