Open challenge rank limits don't seem to work consistently

I have had this happen before, but today it did again, so I thought it worthwhile to bring up. I had set a challenge out there for ranks between 12 and 20k for a live game (5 min + 5x20 byo yomi), and got a player with the following ranks: Overall is 11, blitz is 14, live is 11, and correspondence is 15.

Can someone please tell me what rank is looked at when the rank limits are considered in open challenges? Is it the one that corresponds to the average time per move (which is what delineates blitz, live, and correspondence on the graph of open challenges)? Is it the overall rank? Is it the rank that corresponds to the “Game Speed” selection in the window used to create the game offer? Which? In my case, my game was clearly in the “Live” category, and “Live” was the choice made in the “Game Speed” selector.

In the case of the game today, the rank of the player who successfully accepted the challenge - whatever criterion is applied from the above options - didn’t fit into the range set. Why is it that the system sometimes seems not to pay attention to the limits?

I thought I had this system figured out, but then this challenge acceptance came up, and I just don’t get it any longer.

Any help in understanding what’s going on would be useful. Thanks