Hi
In Windows 2008 and above SAPMNT share folder was created in the virtual name of the SAP cluster group(Not on physical either of the nodes).
You are going to install the second SAP Standalone system on either one of the physical nodes(Not on Cluster ).in that case share going to create on physical node(Not on SAP cluster group)
For example-
1. Existing Two Nodes Failover Cluster system.
Two Node windows failover cluster systems Physical Node A & Physical Node B
Share folder for Cluster environments - in Virtual Name - C (SAP Cluster group)
For cluster system all the share created on Virtual name C (Not on Nodes A or B)
2. Either one of the Nodes Standalone SAP instance
You are going to install the second SAP Standalone instance on either one of the Nodes(A or B). all the SAPMNT share start+ instance profiles are going to create either one of the Nodes(A or B), In this system your are not used the existing cluster instance numbers
Regards
SS