When you create a RAM Disk, the amount of RAM reserved for the virtual disk is reserved exclusively for the disk and no application can use that amount of RAM as RAM. It has got nothing to do with the amount of memory the application uses while loaded/running. So, if you have 2 GB of RAM free and BH uses 1 GB on load/playing and you reserve 500 MB for the RAM disk, the RAM usage when BH is loaded/playing will be 1 GB + 500 MB. The 500 MB that is used is treated as a HDD and BH [or any other application] is not allowed to use that as Random Access Memory.
If you want to keep the full BH player folder in a RAM Disk and load BH from that RAM Disk allocate around 125 MB of RAM for the RAM Disk [the BH player folder takes ~88 MB of space]. More than that is wasted RAM, IMO.
Edit: Some RAM Disk creation programs allow imaging and mounting/unmounting the RAM disk and it's image automatically between reboot's so if you find the RAM Disk beneficial maybe you can think of creating a persistent RAM Disk. That way you eliminate the hassle of copying the BH folder each time.