Ok, now that we have discected to the Nth degree the reasons why track is at different heights, how does that relate to the topic of making a model RR transition? IMHO grade changes in yards on the model is not required as it serves no purpose whatsoever from any operation standpoint (not counting a model hump yard- that’s a different animal), but it adds visual interest and for that it’s probably a good idea to lower the grade of the yards on a model RR. The transition to the yard is determined by the space you have keeping in mind that our models are not as forgiving of track defects and wierd geometries as full sized trains are, so a smooth transition is a must.
Isn’t model railroading more fun when you delve into understanding prototype operations and practices? Now when people ask about your model yard you know how to believably BS them about real yards!