Poor P3700 performance within Hyper-V

I'm scratching my head over this one. Any suggestions are welcome.

I have a single Windows Server 2012 R2 VM using SCSI and a fixed disk within a Hyper-V host. The VHDX is the only VM on the P3700 storage. Performance benchmarks using Atto are very low compared to the advertised specifications for this drive.

Am I missing something? Does the P3700 need to be formatted using a non-standard block size? Thanks for looking!