APM - Cannot allocate lease pool via Variable Assign Action

I am trying to assign a lease pool for Network Access and wish to override the pool assigned to the Network Access profile.

 

There is an article indicating how to do this for a particular IP address which does work. http://support.f5.com/kb/en-us/solutions/public/13000/300/sol13300.html

 

I'm trying to follow the this but update the session.assigned.leasepool variable overwriting the default rather than the session IP address. I basically want to have one Network Access profile but use a branching path to assign different pools to different groups based in the path it has followed.

 

I can get the variable submitted and I can see it in the variable list for the session but for some reason it still defaults to using the IP address from the original lease pool and not the pool i have submitted.

 

I have tried a combination of various things in the custom variable and custom expression and getting different errors and things but nothing works.

 

Not really being super confident with the variables actions i was hoping i'd just be able to wing it but no such luck. Any ideas ?

 

Thanks