MainStage 3: polyphony drops down on upper keyboard.

I have two controllers connected to the Main Stage 3 (actually two Novation Impluse both configured the same)

It happens that with Synths Sounds (example with Classic Synth sound MASSIVE SAWS) when i play it with the lower keyboard it sounds fantastic,

when I pass the sound to the upper keyboard polyphony drops down and chords sound awful.

Please how can I do, for it sound as good in the upper keyboard as in the lower one?

Thank folks!