When I configure the variable speed port on my Apex, it works normal when I set it below 50%. It's almost as if it is scaling all 100% of the pumps power in numbers 1-50. As soon as I set it to 51% it starts ramping the pump back down. If I set it to 100% it turns the pump off.
So the pumps power settings seem to be as follows:
Apex: 0% Pump: 0% power
Apex: 10% Pump: 20% power
Apex: 20% Pump: 40% power
Apex: 30% Pump: 60% power
Apex: 40% Pump: 80% power
Apex: 50% Pump: 100% power
Apex: 60% Pump: 80% power
Apex: 70% Pump: 60% power
Apex: 80% Pump: 40% power
Apex: 90% Pump: 20% power
Apex: 100% Pump: 0% power
Hope this clarifies.