Tweaking FAST.com settings?

I have recently had FTTP installed and after a very long fault finding process, including the provider engineer being flummoxed, it transpires that the only speedtest site that reports a correct 900mbps download speed is fast.com. This is due to its ability to have multiple threads configured as part of its test.

I have enabled fast.com but I am only getting 300mbps instead of the anticipated 900mbps. This will be because I need to increase the number of threads that the test performs. Does anyone know whether the HA fast.com function can be configured to include a specific set of threads, and also a min and max time for the test to take place? These features are available on fast.com GUI, but the HA documentation doesn’t make reference to them.

Many thanks