I'll try this suggestion one more time:-
I'm sure all clan leaders find it a struggle to create fair challenges for their higher rated players.
I have to resort to looking at the players tables only to find that players with similar ratings are a)not in a clan
b)in a clan that's been inactive for 2 million years.
c)in an active clan but continually unavailable(presumably just playing "league"
All I ask is some sort of marker on the players table which shows preferably clan members active in challenges.
Even a marker that says they are in a clan would help.