I think the exposure I calculated was correct.My experience with the R72 is with a mirrorless Olympus.You can focus with the filter on with the live view boost on.I don't believe the R72 causes misfocus on the drone but ICBW.
I can't speak for your camera, I can only tell you that using film day light and a standard slR and lens, daylight has a set focus point. If you left the camera and lens setting fozen at that focus point, when you put an R72 filter on the lens, the IR light is not the same as normal daylight that our eye sees and it does have adifferent point of focus. I am sure all these years the camera makers and lens makers did not choose to put that IR focus point on the lens just for fun and to make it more colourful.
It was there for a reason and any old photographer who may have shot IR or knew enough back in the day, to understand IR photography, will also know that once focused on your subject matter, when you put the IR filter on the lens and everything was locked down, you moved the point of focus showing on your lens, that little bit to one side to line up with the IR lens marking, in order to achieve perfect focus in IR. Maybe do a google search on the subject. When you have a camera converted to a dedicated IR camera, and I have one, you don't need to do that. Plus you can shoot a horse cantering past and freeze it in IR, which was not possible without blur with a normal day light camera, when using an IR filter on the lens. Look through an R72 filter and see just how dark that is, you can not use your normal day light setting for such a filter on a non converted camera.
Here is something on IR photography for you...
Infrared focus marks on lenses
Many manual focus SLR lenses have a red mark offset a little from the regular, white focus mark – normally a line, diamond or dot – to help the user achieve proper infrared focus. When an infrared filter is attached to a lens, all visible light is blocked making it impossible to compose and focus through the viewfinder. To compose and focus, the infrared passing filter must be removed. When desired focus is achieved, the infrared filter should be reattached. The focus on the lens then has to be turned by the difference between the current visible focus and the infrared focus mark.
As mentioned before, this is because in many lenses infrared light has a different focal point than visible light. Most modern lenses do not include infrared focus marks. Many older zoom lenses had two IR focus marks on them – one for wide and one for the telephoto end. If the photographer were using a focal length between the widest and longest setting, then they would have to guess how far to shift the focus, normally around the middle of the two infrared marks.