Dual Plane vs Single Plane Manifold with TBI

I have read countless threads where its said that the divider needs to be milled down if running dual plane. I think engine masters did a dyno test and was having issues until they milled the divider. I dont know if its true but it seems to be common opinion.
I have msd atomic on my swinger with an air gap intake, divider intact. Have not driven it so it can learn. It does have problems coming back down to an idle off revs. A couple feathers and it idles down and will idle fine after that. Im hoping it will tune itself and that will go away. Maybe I will have to mill the divider....hope not.
If your intake is off the engine I would go ahead and mill a slot in it. It wont hurt anything and it will eliminate having to do it later if your having issues with the FI.