Before you go adjusting anything, are you getting snipe with a short board, say 450mm? If this is okay, then the issue is with thicknessing long boards. The Metabo has little support for holding a long board coplanar. The end drops, and is pushed into the blades.
The fix is quite simple - support the board as it runs through the thicknesser. The way to do this is lay a thickish section of melamine-coated MDF (screwed to ply would be better) through the bed, and long enough to stick out about 450mm each end. More out the exit end, if you wish. You still have full use of the thicknesser, just a slightly reduce thickness (there usually is more than needed anyway).
If this sorts of the snipe, it is evidence where the fault lies.
Leave the settings along until you try this.
Regards from Perth
Derek