Question re setting correct altitude

I have a large area to map and will require to change batteries etc. I want to ensure the Mavic Pro is correctly focused so always switch to DJI Go4 app to manually set the WB, ISO and focus. I do the focusing ‘at height’. I then switch over to the DD app, and run the flight. When I switch over batteries and carry out the same focusing procedure in the Go4 App, do I have to be at the same altiutde each time in the go 4 app - before switching over to DD and continuing with the flight? Obviously I need the set altitude of the flight plan (75m) to be equal throughout each section of the flight…
I think I have made that sound more complicated than it is but if anyone understands my questions please assist…

At least close so the focus is the same.

@surreyvisuals, can you report on your progress?