Sheez BEagle, that was quite a masterpiece
FL, see my earlier piece regarding the Standard Closing Angle technique if you are still a bit unsure.
To get back to the original question, this thing about hours is quite simple. The CAA deem instructing as non commercial, only aerial work, but instructing at an 'Approved School' (what we knew and loved as CAP509) IS deemed commercial so CAP371 applies.