Technically five should be the maximum per KH as there are just five working days available for evening meetings. The "sunday" meeting is possible to arrange on saturday also, so they could split it ie. two on saturday and three on sunday. Ofcourse if the congregations would be built based on segmentation, you could also start daytime congregations for retired, unemployed and similar groups. If we consider four meetings per weekend-day as practical maximum (10-12 13-15 16-18 19-21), you could actually squeeze in eight congregations to one KH, just you would have sufficient amount of people for three daytime congregations.
Today again in speculative mode
CP