I've noticed that by default VV saves activities with a reduced amount of data points. As a result the stored activity is made up a number of straight lines, rather than following the curves of the road/path accurately.
If you open up the specific activity in VV it then fetches all of the data points and a far more accurate track is stored.
I did this for a few of my activities and hey presto, I have dropped from 56x56 to 45x45
So it seems a ride out to Petworth is required!
I wonder how many other "fake" tiles I have? I contacted Ben at VV to ask him if it was possible to trigger a mass regeneration of all activities. He said it's not and one would have to access each activity individually to trigger a recall of the rich data.
+2000 activities will take some time.
I'm fairly certain that the activities done specifically to target tiles are good. But there could be quite a few normal rides that are not. It would be a nice project to find all the holes and fill them.