SQL Server 2008 R2 VM only seeing 4 CPU's

Hi All

I have SQL Server 2008 R2 Server / CAL SQL licensing

I have a Server 2008 / SQL Server 2008 R2 VM Guest 

Host is Hyper-V 2012 with 2x 6 core CPU's with HyperThreading, so 24 logical procs

I have allocated 10x CPU's to my VM'

They all show up in task manager as expected

If I look at the properties of the SQL instance, it only show's 4 CPU's listed, not all of them

I thought if I was under Server / CAL licensing then I could use as many CPUs / Cores as  I like in a VM?

does anyone know why it would only show 4? it sounds like its been configured as a Processor lic, not a Server lic, if that's the case, how do I change it?

The reason I came across his issue is I notice that the SQL server was only using 1 thread, I assume that is another issue though?

thanks for your help