First of all. The gridlocations you get ordered to patrol have no relation to whether or not there really is traffic at all. It's just some grids the game selects one from based on Flottila and date iirc. Think of it as Dönitz' tactical desiscion. And he was forced to guestimate alot anyway in the absence of straight intel.
Don't forget traffic comming from the western shores of Africa going towards the Brittish Isles. The amount of routes going that way (including the ones originating from the Med.) is several gridspaces wide, almost as wide as a complete BF grid, or a grid the size of the Spain/Portugal Peninsula. So just considering BF47 being on traffic routes or not is a far to narrow scope.
The convoy map doesn't do justice if you compare it with the massive bundle or routes in the campaign editor. I know you didn't want spoilers. But looking in the random generated script layer zoomed out (and without year filter selection) you'll never get a clear idea as to where each ship/convoy will be. Too much data overload. It doesn't show the gridsquares either. That's also not even considering random waypoint choices most units will make along the way.
In short: Don't second guess Unkel D. You'll get bored anyway waiting for something to pass.
