I tried flying manually, but there was too much wind that day to get anything usable.
Then I tried using Pix4D, but as you found it isn't useful on small precise tasks like this. Neither was DroneDeploy (for the Surface Overhead), but sounds like they use it for a orthomosaic of the overall site.
Then I spent way too much time setting up a way-point mission in Litchi, with lots of waypoints to take photos along the "lawnmower" path. This would not be practical to do for the money they are paying. I have not run it yet to see how it works out.
Also just used the new DJI GD Pro to setup a mission, but haven't figured out how to control the camera to take the overlapping photos over the route. Will poke around with that some more just to learn the new app.
Seems like I may be overthinking this, in relation to the financial payout...