Thank you for sharing this great post!
From my experience (oblique and UAV-based imagery) there are only tendencies and not fixed formulas which should be used. For instance, for many small (< 100 21 MP images) oblique models, I usually get best performance by doing the following:
1) Set the max number of key points to 1 mio to ensure that all key points are generated. (As Marcel pointed out, 21 MP images will max out at a much lower number, but 1 mio just sets the threshold to "max")
2) Set the tie points to 0
3) Remove sparse points using gradual selection at 1 px or less (Marcel used 0.5 in his tests)
4) Optimize cameras
5) Repeat steps 3-4 until the reconstruction error is minimized
Depending on the imagery, a sub-pixel error of 0.5-0.1 can be achieved for most of my models. This takes a little more time processing at the onset, but the georeferenced model at the end is usually of a very high quality.
Here is an example of a small Austrian river made using the above workflow:
https://sketchfab.com/models/6c82e6f76167440cbff60862ea418f15Jeff