intergrated cooker hood question

[hardtail]

hi guys im going to be fitting our new kitchen wall unit tommorrow and also a cooker hood which ive never mounted before ,i have place a hole ready to vent outside and it is level with the top of the units and i will be using 100x50 ducting resting on the units ,now do you usually mount the extractor below the height of the units to allow the elbow for the ducting to be hidden behind the facias door many thanks in advance

 

[PrenticeBoyofDerry]

What do the manufacturers instruction say?
I don't quite understand what your asking, cooker hood type, pictures of the area too, might help understand.

 

[foxhole]

Please read you post and amend, is a little garbled?