Peter - I think you mentioned the wrong config.ini parameter.
The one you mentioned is autodetected.
prefvmx.minVmMemPct = "25"
can be used to overcommit memory - it allows to swap out most of the VMs memory.
It might be autodetected initially, but can be overwritten manually.
This is the only parameter, that will force to use host memory management, rather than VMware memory management to overcommit memory used by guests.
prefvmx.allVMMemoryLimit = "xxx"
This option limits the host memory that can be used
by all running virtual machines. It will not allow
over committing host memory.
That is contrary to my observations. In a situation when this value was autodetected to 370, I have increased it to 450 on a host with 500 MB RAM.
Host started to use swap, to manage increased application memory requirements. With default 370, VMware was not allowing to increase combined RAM size for guests. With 450, I was able to add 80 MB to my guests. That is all done with guests set to "Fit all virtual machine memory into reserved host RAM" setting.
Obviously if you want to use VMware memory management, you can do what continuum said, or just select "Allow most virtual machine memory to be swapped".