In order to keep the flight planning consistent make sure you are selecting "Custom Camera" as the camera model in the Map Pilot settings.
Map Pilot does not help you calculate the image footprint dimensions for external cameras. You can plug in the sensor dimensions, pixel pitch, resolution and lens focal length and Map Pilot will take them into account when planning the flight path.
You are on your own for executing that unless you are using our Ninja OBC which manages the triggering using distance.
You can figure out the distance by which the images should be trigged on your own using our point estimator. You need to supply the sensor parameters, focal length and flight altitude and it will calculate the spot width and height for you.
If you are looking to trigger for 75% along track overlap you can trigger at 25% of the spot height number.
If you don't know your position and can't distance trigger you can use the maximum speed of the flight to back out a triggering time using that same distance.