Mosaic 2x2 with LNC issue

Hello:

I have tried a lot of different ways with this 2x2 mosaic, but I always get this inner background issue with it turning out like the image.  I have used LNC heavily, 1st, 2nd, 4th and 3 to 6 passes, doesn't matter it is always about the same...

I registered the sections individually and stacked them, then I take the 4 quadrants and combined them into the mosaic with multiband blending.  Scale start is 5, scale stop is 15, I use DDC and no same camera optics.  Everything else pretty stock. I thought LNC would take care of this?  the individual panels look good, so not sure why they do this when I go mosaic with them?

I stretched it out so you can see here the brownish areas.