Thanks to Bernie Mayoff for producing these three projections of the Belarus area and the Mayoff shtetl of Kostyukovichi.
You'll notice that there are two different Kostyukovichi locations approximately 150 miles apart.

 

Which one is our ancestral shtetl?
Bernie Mayoff has pointed out that the more southern location is rather close to a town called "Mazyr" [also recorded as "Moyzr" in some references] and a possible root for our family name.