I've played often with friends and solo in ranked and solo queque matchups, and like in more than 30 games, I haven't received any key fragment, I know that key fragments had more drop rate if you play with friends, but more than 30 games and no key fragments. I don't know if my acc have a problem or I have so much bad luck, because the boxes are so easy to get when you have it available.
I know Rioters that the drop rate of the keys is low for more than anything marketing reasons, but I feel is harder to get a key fragment than a box, and for me is taking too much time.
Mind you, if you can clarify me the drop rate with numbers or telling me if something wrong with my acc? or what rank in game give more chances or if I have to play different champions?