Hi Betty,
The marriage of Joseph Bing and Mary Allen sounds like a very good lead particularly if there was a Joseph amongst the children of John Macey and Sarah Bing. I would suggest though that, in addition, to looking at Joseph Bing as a potential brother, you add him as a potential father, uncle or cousin to Sarah.
From my own database, I've found a christening as follows:
MACER, John C 17 May 1747 son of Nicholas/[wife's name not recorded] at Aldington. Source: BT
There is also this christening from my database:
MERCER John C 10 Feb 1754 son of John/Mary at Pluckley. Source: BT
Although the first above listed John would have been a little older than he would have been if born circa 1755, Aldington is another parish that is 21.7 miles distant from Deal while Wye is 20.2 miles distant from Wye.
Within a 13-mile radius of Deal are 95 parishes most of which are not on the IGI. Within a 7-mile radius there are 34 parishes, likewise largely not on the IGI.
I can eliminate all three parishes of Sandwich for you as those are part of my database and there are no Macey [variants included] living there.
When you say you went through the microfiche records, did you keep a log of which parishes you did? The following is a list of the immediately abutting parishes to Deal and as you can see these have not been indexed on the I.G.I. Even if you have done each of these parishes, the list may still be useful for someone else researching Deal and wondering 'where to next'.
Do you use the Parloc program
http://www.parloc.pwp.blueyonder.co.uk/ to help plot neighbouring parishes?
Betteshanger not on igi
Northbourne no igi
Little Mongeham no igi
Great Mongeham no igi
Nonington - on Kent-opc.org and nothing there
Ringwould no igi
Sutton no igi
Ripple no igi
Tilmanstone no igi
Knowlton no igi
Waldershare no igi
Chillenden no igi
Eastry no igi
Worth no igi
Woodnesborough no igi
West Langdon no igi
East Langdon no igi
Oxney no igi
Shoulden no igi
Regards,
Susan