There was discussion about what should be the line judges reference point for calling over early or finishing for a boat. Was the sighting of the top center of the mark the proper reference or was it the forward edge of the mark? Some said race committees were not doing it properly. The answer for model yachts is contained in Appendix E of the RRS.

E3.7 Starting and Finishing Lines
The starting and finishing lines shall be tangential to, and on the
course side of, the starting and finishing marks.

So the answer is- Tangential means connected to. This would mean that the Starting Line and Finishing line would be the side of the buoys on the course side. The edge of the mark on the course side.
Line judges should not be sighting the top or pin of a mark, but the leading edges. Harder to do, but the right method. Competitors trying to thread that needle need to be wary as only someone exactly on that line with clear line of sight can make the reasonable judgement.

I will add here Tom, that if it is properly stated in the SI, the race staff may use a different part of the mark if it is better (easier) to see or judge. For example, some clubs use those triangle marks that are made of two flat plastic of metal panels sitting on a foam ring. It is much easier to sight the top of the mark at the point than to see the leading edge of the foam disk which is just above the water. Plus if the mark spins, it changes the leading edge of the mark. I do not care for it, but so long as everyone understands ahead of time and so long as the race staff are consistent, it is ok.

That said, at our lake we use round marks and always call the course side.

Ok, I just called on my previous comment. What I mean to say is that your SI should not restate any rule that you are NOT changing. So in the case of Florida and the start and finish marks, we sail exactly as rule E3.7 states. However; if a host club has those marks I described and they want to use the top/center point of the mark or what have you, they NEED to spell it out in the SI that they are modifying Rule E3.7 and explain how they will judge the line so that every skipper knows in advance of the racing.

I hope this is clear now.