Thanks Jorge,
You are suggesting that the best way to get a good orthoplane is to take the imagery from the same desired angle.
I was afraid this would be the case. This article (https://community.pix4d.com/t/5934-Orthoplanes-using-a-combination-of-terrestrial-and-aerial-data) suggests that the algorithm that chooses the (best) image is heavily biased towards ray angle over proximity or GSD.
I probably won’t have time to re-run the project with vertical grid flights around the project site, but will try and do this next time although the number of pictures (and processing time) then increases significantly. Having said that, maybe having only one camera model in the final project then makes processing easier.
Thanks for your help.
Any other recommendations for getting the best without returning to the site?
Charles