If you dont do large HF’s, camera distance can probably stay the same. Its easy to determine the magnification factor - lay a ruler at spindle CL under the lense, then measure on the screen. The ratio of the 2 values is the magnification.
Rather than drawing on the screen or overlay I made a target template on the pc, cutter at center and concentric circles for different wall thickness, all adjusted for the mag of my camera. I have different templates for different cutters. I only use a 6mm and 9 mm round cutters for this. Templates can be made for different camera distances. It was funny when I asked around at work for “transparencies” to print on - no one had heard that word in a few years.
When the cutter gets repositioned, the camera the is moved to align the center on the cutter. I use a Jamieson system with the camera mounted to a dowel through the laser clamp. At times the cutter gets 2+ inches off CL. I move the support arm over to keep the lense over the cutter to maintain correct perspective. The center circle matches the cutter so cutting edge orientation, such as around a corner, doesnt matter, no adjustments necessary. The advantage is the template is already made, with concentric line for different thickness, no drawing for different wall t or different cutter orientation. My stack of printed templates should last a lifetime but I can always print more.
Regardless of the method used, always pull the cutter out occasionally to check camera/cutter alignment. The only time Ive lost a piece using the camera was when things shifted and I went through the wall.