Well what it comes down to is the previous HH lids design.
The newest heavy harvest lids are shaped a bit differently to help prevent the plants from caving in, the first heavy harvest lids fit good when there was no water in the thing, but when you have water in the module it causes the module to bow out slightly on the sides. The new lids are wider throughout the middle to help this problem.
what was dans recommendation by the way?, cause the first system I got has the original design HH lids, then the lids I ordered a couple weeks ago are the new shape.
Do you know if you have the Original HH lid or the Newest HH lid?
the original are 13" wide, the newer ones are 13 1/2" wide and more rounded.
*edit,
guess u don't have the HH lids, my bad.