Host Cluster Over-committed with spare memory?

I've encountered an issue on SCVMM 2012. When I attempted to place a new VM on a Hyper-V cluster, there was an error "This configuration causes the host cluster to become overcommitted". I checked all the node properties and realized that there are still more than enough available RAM on each node. Why the overcommitted problem?

I came across the Technet forum page where Mike Briggs explained the memory calculation of SCVMM. First, SCVMM would sum up a new total memory requirement by adding up all memory used by all existing VMs and the new VM requirements to be deployed. It would then calculate whether the host cluster able to withstand the new requirement if the specified number of node failures are allowed to fail. The number of nodes allowed to fail is configured in the cluster reserve.

If you are confident of the overcommitted issue, simply adjust the cluster reserve number downward and the VM placement would continue successfully. The reserve number can be found on the the General tab of the host cluster properties of SCVMM console.