Chuck;
Those angles were taken directly from the L C Smith drawings.
Note that SAAMI drawing is for a "Minimum Chamber". I believe they are saying that is the steepest angle (Shortest cone) they recommend, not that it should not be exceeded in length.
Based up on actual chamber & bore dimensions the small (Forward) end of most chambers are approximately .070" larger than nominal bore or .035 per side. 1/X Tan 5° x .035 = .400" for the length of this cone.
The trig is good, the fallacy is in assuming that 5° represents a modern long cone. A 1˝" long cone with .035 difference per side between chamber & bore would be an angle of 1° 20' 12".

Miller/TN
I Didn't Say Everything I Said, Yogi Berra