Opella toilet syphon

Hello,

I fitted an opella toilet syphon a few years ago it has never given a complete flush both of the blue plugs are in place should I remove one or would that make it worse.

Once flushed the water level is just below the lower of the 2 blue plugs leaving approx 2" of water.

Should all of the water be emptied from the cistern?

Thanks
Tony

did you get instructions, those holes , operate the amount of flush - mine was something like, 9L , 6L, 4L settings
cant find the one for the Opella , but the thomas dudley are here - which i think i got from screwfix

Not sure about if I had instructions was a while ago , is it normal to have approx 2" of water in the cistern after its been flushed?
Thanks