ziggity:
https://github.com/FAForever/fa/pull/5653
None of that BuffBlueprint bs (that probably won't work, as Jip surmised), but we can bypass the problem entirely by simply telling the transports to unload when they're very close (1-2 ogrids), as opposed to the extremely close currently asked for by the engine (<1 ogrid).
With a little flexibility ("little" as in, a rounding error compared to that introduced by a group unload order) in the dropoff point, we're free to adjust the flight performance parameters to whatever we like. See the Courier in the above PR.