i have found that if i put food on all hives, the robbing problem is not an issue. i have 3 that need feeding right now, but i have put food on all and there is no robbing. in the past, i have only put food on those needing it and have had problems.
the syrup will not be wasted because i'll take that unfed syrup from those not using it and put it on those that need it. fresh on those that have not taken it. in the end, it all seems to even out.