BillO:
I'd be tempted to use the little cylindrical magnets at the top left of that page. They will have a more narrowly defined field.
I hadn't settled on which magnets, specifically. Those were handy as an example of the sort of gauss strength I was looking at, as a 1st pass. It looks as if I'll end up ordering from Digikey again, just because they have everything on my shopping list, as opposed to Tayda, e.g. But you're right that smaller will be easier for me to deal with.