I'm not sure how far you live from the Kent GS' but bear in mind that considering the oversubscribtion criteria a pass will not be good enough, one would need a high score to get in. Kent sort of prioritise their own residents, rightfully so imo, unlike Bexley.
True, a high score is required for out of catchment children. However, so it is for OOC children in Bexley. To be assured a place you'd have to be on the top 180 which I think works out as the top 2%. Of these top 180, I reckon no more than 80 choose the Bexley grammars. This at allocation time. We'd have to find out how many of those actually take their spaces in September and haven't gone elsewhere. We know that the Bexley grammars allocate spaces even after the term has started. We don't even know where these top 180 come from. They can be Bexley residents going elsewhere. So, in short, I do think that Bexley gives priority to their residents.