All of that dreadfully complicated and unnecessary. Tangents??
1 in 60 is your friend - heard of that? By the way, stick with Altitude/3 - it is far better!
Just stick with that. You can do the maths if you wish, remembering 1nm is near enough 6000ft. but much simpler to learn the 3 times table.
Thank the Lord for nautical miles
What those strange Europeans do I do not know.