Anything under 15 yards can be a spot foul, that's not an issue. If your WR is getting interfered with 47 yards downfield, then he likely wasn't open in the first place.
It bears repeating, if your WR truly has the DB beat on a deep route, and the pass is accurate, there is nothing the DB can do about it. He can't tackle him. He can't even touch him. And if he can, then either a) the WR didn't get separation or b) the pass was poorly underthrown -- and in either case the offense doesn't deserve to get 50+yds of offense on a flag. That's the cheesiest play in football, and it's happening more often every year.