I've configured the VMDX files to use expanding files, with each file being limited to 2GB.
From a defragmentation point of view it is better to use fixed size virtual disks, so they will not get fragmented and you can run MyDefrag less often.
leaving approximately 5GB of free space after each directory.
Feel free to do so, but sadly enough Windows will not (always) use that space when a virtual disk needs to grow.
p.s. It is also important to run MyDefrag inside the virtual machines, not only on the host.