How high is "up"?
Well, while I was coordinating my coordinates I figured I might as well toss in elevation, Chicago averages about 630 feet MSL, divide by 3.3 to get heathen furriner metric numbers comes out to about 190 meters plus a Belgian waffle with two Scottish groats change. More or less.

Dunno what effect that has if that's set before starting the route, but changing it on a half built route is apparently not a good idea.
Get height gets the height MSL, instead of zero now it's 190. Okay, use height, 190 above what is already there.

That don't work for leveling terrain under assorted buildings, so let's see if we can change the bird bath to reset to zero.
Cripes, the little culprit skipped town. Dunno where it went, so try placing another one;
And that works, now zero is zero again.
All this seems to me to be a lot more confusing than it needs to be, if the get height tool uses MSL elevation why don't the use height tool do the same? Why do you have to place the birdbath in a session, does someone need to move the route from Halifax to Hong Kong between sessions? If they do it won't work, the numbers you set in the session are stored in the route, you have to choose either Halifax or Hong Kong anyway, so why not put the birdbath in the route layer to begin with?