I assume that washers could also be used with the top mount that was tested to MASH.
I have included a drawing (bottom view) of how much room the washers have between each other. A ½” inch between the washers don’t allow for much tolerance if a contractor has to drill the holes in the concrete.
Is it possible to make the gap between washers larger?
Washers could certainly be used. 6”x4.5”x1/4” washers were used on the original system. We don’t see a real issue with reducing the washer width to 4” to allow for easier placement and installation.
One item to note is that the washer size was selected to ensure that they provided bearing if some of the concrete spalled out during drilling. Thus, you may was to note that if the washers can’t effectively span the concrete spalling areas, then larger washers or a single plate washer should be used.