In relation to the homepoint such errors make no difference.
HOWEVER if they influence the actual height at which it RTH's then that's a different matter entirely. Mind you, since they are indicating low that's possibly in the 'safe' direction.
Could you set your RTH height to the height of a 'tall' object then fly to a point that would give an RTH path into the object or close by it? Stop the RTH before the drone gets too close to the object then see if the drone is level with the top of the object.
You should practise stopping an RTH before trying this so that you can see how to do it and judge braking distances etc.