Eureka! Despite tooling around in Templot, I still couldn't come up with a shunting zone track formation that I was comfortable with. Being able to customise things certainly helped, but it didn't cure the problem. The root of my difficulty is that the baseboard isn't wide enough for what I want to do, largely because it only just accomodates the curve of the track even before I start adding sidings and run-rounds. So the obvious solution is to make the board wider. Quite why I didn't do this straight away I don't know, but the finger of suspicion is pointing at the industrial quantity of Chateau Screwtop in the kitchen.
So the supports for the middle level viaduct have been moved over enough to allow an extra couple of inches of baseboard to be inserted. Although the track itself will barely touch this, the extra width does let me slide things around enough to make a workable track formation (without recourse to track-building) and still have space either side for scenery. The key gain is the ability to place a run-round loop toward the back without interfering with the sidings at the front - previously I was trying to squeeze too many points into too little space.
Contrary to what I said before, I've found I can just about photograph the whole area, although it involves some gymnastics that I'm not entirely comfortable with. Still, as the air is getting slippery up in the loft now, that'll be all the modelling I'll be doing today and I can have a rest.
Finally, just a quick snap of what happens in this weather if you don't fix your track down and leave enough expansion gaps. This is (fortunately) just a section of temporary track, so it was left loose on the baseboard, but it's quite alarming how it tries to climb into the air because of the heat!
Currently On My Stereo: Les Claypool - Of Whales and Woe