50x11 speed vs cadence on different gradients

On my so called smart trainer controlled by Zwift, I can be doing a cadence of 110 on 50x11 gear ratio and do 27 mph on the flat, then the same cadence on a downhill is equal to 40mph. 

Is this normal behaviour for a Zwift controlled smart trainer? It’s an Elite Real Turbo Muin Smart B+ which does increase resistance depending on gradient, but no where near enough, which is a whole different issue. 

When you’re in the game you can go into settings and increase the difficulty level, which may give you more resistance. 

Sorry forgot to mention, I have that set to 100%

Before the controlled trainer, effort/power equalled speed in Zwift. But with ANT+ FE-C today, I would expect cadence & gear ratio resulting in constant speed and effort/power depending on resistance (drag and topography)