12 planes at 20K is indeed a horde.
First, thank you for explaining to the AH community how many planes constitute a horde. Second, I never knew that altitude plays into the making of a horde, but coming from such a reliable and respected source it must be true. I do have a few questions for clarification though:
1)If 12 planes are at say 19k, then they are not a horde?
2)If 11 planes are over 20k, then do they become a horde?
PS-Have the ground crews check your altimeter Sunfan, as i believe it may be off by about 5k!