I think that having it vertical to the direction of view might upset the operation of the compass/gyroscope/inclinometer and that flat along the top of the tube would work better since it is face up and flat the way it is when u hold it. May not be necessary and just my wrong view of things though.
I just bluetak mine to the top of the tube, but being a mak this is not inconvenient to use it this way.
Interesting to note too that in the video link I posted, an LG failed miserable at calibrating the compass.
Here's an interesting idea on mounting Skyeye on a tube on a Galaxy Tab
https://www.youtube.com/watch?v=B2k_oWac-pk
Julian's comment about Sensor Fusion is also important. I found Normal to be far better than more sensitive setting.
Trevor