The one spot is deceiving as well. The last large batch that went out, multiple facilities with one slot were assigned multiple people. The only reason they reserve one is so it doesn't drop into the next academy list. Places like JAN and MWH had multiple spots so close to the top, they had to reserve multiple spots to make sure it didn't drop into the next academy class in case 2 or 4 people actually want those places.
They will fill spots directly based on your ranking list. Ex. the only way you'd get your 9th choice is if there are no spots remaining for 1-8. Not to say that it can't happen, but up to this point, the lowest that I've seen a candidate fall is to their 3rd choice. If anyone does not get a facility in their top 3, I'd like to know to better inform candidates down the road.