Geodesic domes get their strength by being self adjusting.
They are not true structures if you define a structure as a thing whose parts do not move relative to each other.
Geodesic domes are always vibrating about a mean and so unlike rigid structures they can self compensate.
This aspect of geodesic dome is not at all captured by FEA software and therefore it fails to forecast the correct strength of a dome.
Anyway about 11 degrees roughly will do well for domes of your size.
Regards
Ashok
Sent from my iPhone
1. I see calculators for lengths of struts but what about the angle to end the ends? Ive heard 11 degrees before but no idea if that applies to that persons specific plan or not.