JSJ Hi Joe
Yes, this is a real Standing Agreement! 7 miles before Avant is about 10nm before the sector boundary between S19/S25. No idea why this was chosen, but no doubt the people making the procedures have their reasons for this. I would imagine for the following reason: it must to be level no less than 5 nm miles before the boundary in order to be separated from traffic unknown to S19 operating in that area. Add a bit for traffic descending slower than required and not making the 270 in time, there is 5 nm reserve that way. Don't forget, at 300 kts, 5 nm is only 1 minute flying! But again, this is just my thinking.
cheers, C