It sounds like the coil alone can have up to .8 inches of static & that's a pretty good amount of allowance. It doesn't say anything about tsp but my understanding is that most VS motors max out around .8 to 1.0 tsp on AH's with coils. That cabinet can be set to put out anywhere from 800 to 2000 cfm so its possible the system is just not setup right.
The MBVC blower cabinet uses a variable speed motor that
maintains a constant airflow with a higher duct static. It is
approved for applications with cooling coils of up to 0.8 inches
W.C. external static pressure and includes a feature that
allows airflow to be changed to + 10%.