I was honestly even more aggressive in this design myself, and even if I never suggested a fixed number, following Tom's advice I'd go for even bigger numbers, like 10x. The reason behind this is that any large virtual machine entering the SOBR if it's size is a large percentage of the extent size, it will create issues with the placement algorithm. I'm NOT saying that the algorithm cannot place the VM correctly, rather than calculations about free space will be impacted by this. In Tom's design, that machine alone will change the free space calculation of an extent by 33%, which is a massive number IMHO. I'd go as Tom said with fewer large extents, planning to have a decent number of VMs stored in each extent.
EMEA Cloud Architect @ Veeam Software
Veeam VMCE #1