Juniper WLC Cluster Licensing - How does this work!

THIS IS NOW INCORRECT. SEE THE NEW POST - ThWh 26/04/2013
http://twhittle1.blogspot.co.uk/2013/04/juniper-wlc-licensing-cluster-update.html

I've left this here for the sake of keeping previous information, this may even apply if you are running old code but as above, please note there is an updated post on Juniper WLAN licensing

So I'm working with some WLC controllers and a thought strikes, if I cluster these together, how does the licensing work? Is it one big pool? Is it individual? Or something different? Well I've done a bit of research and here is the answer:

Each WLC in a cluster has it's own license count. There is no shared pool. If a WLC has licenses for up to 96 WLAs this is how many it will be able to manage. Therefore to achieve redundancy you need to ensure that if an WLC was to fail there would be enough licenses left between the remaining WLC to pick up the load.

For example:
A 3 WLC880R cluster has to support 192 WLA access points. You cannot just divide 192 by 3 (=64) and license each controller for 64 APs because you would not have a redundant WLAN. If a single controller failed then there would only be 128 total licenses remaining between the 2 remaining controllers. This means that you need at least 96 licenses on each controller so that if any single WLC failed the remaining 2 would have 192 licenses between then, enough for each WLA.

The formula that Juniper gives to work it out is:
Maximum Redundancy Capacity == total cluster MP license - largest MX capacity

However I prefer to think of it as:
Min No. Licenses per controller = No. Total APs / (Number of Controllers -1)