DDM over SNA - Session Limit Problem

Ok folks...put on your SNA thinking caps if you will. I have a mode
description between two systems running SNA over AnyNet. Passthru and DDM
connections between the two systems. The mode description looks like this:

                           Display Mode Description
                                                            11/2
Mode description . . . . . . . . . :   BLANK

Class-of-service . . . . . . . . . :   #CONNECT
Maximum sessions . . . . . . . . . :   512
Maximum conversations  . . . . . . :   512
Locally controlled sessions  . . . :   0
Pre-established sessions . . . . . :   0
Maximum inbound pacing value . . . :   *CALC
Inbound pacing value . . . . . . . :   3
Outbound pacing value  . . . . . . :   3
Maximum length of request unit . . :   *CALC
Data compression . . . . . . . . . :   *NETATR
Inbound data compression . . . . . :   *RLE
Outbound data compression  . . . . :   *RLE
Session level encryption . . . . . :   *NONE
Text . . . . . . . . . . . . . . . :   This Mode is IBM Supplied

We had a problem with APPN session timeout, which I think may have to do
with the number of sessions reaching the maximum of 512. We put in a
RCLDDMCNV which I thought would remove the conversation and the session,
removing that session from the count. Doesn't seem to be working that way.
The number of conversations is staying at 254, while the session count keeps
climbing.

How do you end a session and remove it from the count of sessions?