That's the problem, the docking unit itself does not count as a docking enhancer, and as such docking enhancers won't group through it.right from the docking unit out
I suppose this is what you have built(O=empty ; X=docking enhancer ; Y=docking module):
X X X Y X X X
O O O X O O O
O O O X O O O
O O O X O O O
O O O X O O O
O O O X O O O
O O O X O O O
O O O Y O O O
X X X X X X X
O O O X O O O
O O O X O O O
O O O X O O O
X X X X X X X
O O O X O O O
O O O X O O O
O O O X O O O