H5 would be halfway from the drop to the end of the main beam. Again, I could be totally wrong.
Don't all deer get 4 circumfrences per side no matter how many points?
And the circumferences are measured between the typical points. A drop tine would not be used as a reference point.
For H measurements up to H3, the measurement is taken at the narrowest point between the two typical tines. H4 would be taken at the narrowest point between the G3 and G4 tines. If it's an 8 pointer, H4 would be taken halfway between the G3 tine and the tip of the main beam.
Now, if it's an 8 pointer with a drop tine at exactly this point, I'm not sure what they would do.