thanks bb2k,
here is the nozzel i am using
at the nozzel end it's a 2mm slit. The main reason for this is to cover the width of the fin base.
i agree with the base plate thickness as my best block so far is the one i took the base down to 2.5mm. this is 1C lower than a maze 3 and also a block i made with a base plate thickness of 3.5mm.
in my test stup i have a aquabee 1000 l/h with 1.5m head pressure.
in my actual pc i have a ehiem 1048 which i dont think will be able to cope with the impingement style blocks.