Slope simulation

I've got a tacx Flux with 10 % slope simulation

When going from 0 to 5 % simulation I feel a great change in resistance

I don't really feel a change when going from 5 % to 10%. The speed in the tacx app changes but not the resistance

To get the same feeling as an approximately 10 % slope outside I have to put my bike on the big gear wheel (I got two) and the 5-6th rear speed 

(Outside I will use the small gear wheel and the 2nd rear speed.)

So i'm quite disappointed and think it provides not that much resistance...

Is this normal and does the slope simulation is also done by using other gears than in real life or does my tacx have a problem ?