71Jeep,
I'm pressed for time these days, but I have a layout in an 11 x 23 space that is 2.5 levels along the long side: that's three levels on one long side, two levels on the other, and transitions along short walls.
I say my layout is Pennsy-oriented; in fact, I have Pennsy painted locos and a fair proportion of Pennsy cars. When I designed it, I was more concerned with the geometry of a long, simple run with some operations whenever I had time to diddle, which turned out to be never.
I left a very wide center space, but even one three-foot bottleneck was--well--a bottleneck. I've described the philosophy over on Trainboard, but can't search for it tonight. Basically I climb along the back of the long walls at 2.5% to gain about 15 inches between decks.
Here's the first level:

And the second:

And the third on the "west" side:

The levels on the west side are roughly 30, 45, 60.
The levels on the east, or bottom side, are 37.5 and 52.5. Make sense? If you are more or less continually climbing, then decks on opposite walls will be staggered--especially when the harbor has to be FLAT.
Hope this sparks some thoughts. In retrospect, this was an exercise in geometry, and a good drawing package (with vector information) was essential in designing it. When the drawing package calculates path lengths, getting the track elevations becomes easy. If you would like to discuss this, it's probably best to contact me at
peterknolan@gmail.com due to my travel schedule the next few months.