Setting connection limit(call limit) to nodes while load balancing sip traffic over UDP

I have the following setup. SIP call is distributed from SBC to F5 LTM over UDP. Created a SIP persistence profile in LTM using call id as persistence key.

Calls are being distributed to all nodes in the round robin and SIP messages are getting persisted.

My requirement is to load balance the calls to the least active call node and limit the number of active calls to each node. i.e Nodes shall take only x number of active calls at any time. Active call is a call to which BYE is not received yet.

Tried setting connection limit to each node but number of connections is always 1 on the statistics page. The connection limit is always 1 as in my case SIP is over UDP, source and destination IP & Port will be same for all calls.

Is there any way in F5 LTM where we can limit the number of calls to each node and load balance the calls to the least call-taking node for SIP over UDP?