Sorry Dan, I don't doubt your observations, but what I said about the origin point is true.
Clam1952's bushes and trees are not exceptions to the rule. The ones that have a single trunk, and an origin at or near its base (which is usually the case), do not "float" on sloping ground.
Those that are a group of bushes will, by definition, have multiple trunks. As such, the origin point cannot coincide with all the trunks at once, so when placed on sloping ground, some trunks will be buried and others will hang in mid air. The origin point, wherever it is in the object, will still be at ground level.
The exact same thing happens, must happen, with any extended scenery object, like a group of trees, a house or a slab of concrete. One side gets buried while the other extends in mid air, but the asset overall is not floating, at least as far as its origin point is concerned. So it's the position of the origin in relation to the visible parts of the asset that controls everything, not whether foliage is touching the ground.
In clam1952's bushes, I noticed that he has tried to alleviate this problem to some extent by making the origin 0.2-0.4m above the base of the trunk(s). This means that when you place a bush, 0.2-0.4m of the trunks (and possibly some of the foliage) will be underground and will not appear to "float" until the ground slope is enough to expose more than the lower 0.2-0.4m of the mesh.
For buildings, it's a lost cause to expect creators to make them all with extended basements. I think a more practical solution is to landscape the the ground and make it flat or place a thick base of concrete or maybe one of those retaining walls with flat terrain attached to take care of the slope.
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