Mercenary Behaviour

As has been mentioned before, the problem is the reward structure. In most events, top 100 or top 150 get the extra cover. Now, since 4* are supposed to be rare, why can't they make it top 75 instead of top 50 for 4* events? There would still be mercs and team hoppers, but it would not be anywhere near as bad. I know a lot of players want 4*s to be top 100 or so, but they are supposed to be rare. So, IMO, top 75 is fair compromise for all.