Recently infused three test panels inside one vacuum bag. All three panels were four ply. First panel was 3K 6 oz twill. Second panel was 3k 12 oz flat tow plain weave. Third panel was 12K 18 oz flat tow plain weave. The first panel full infused but the other two did not. The question I have is did the vastly different architecture of the materials cause the incomplete infusion? What other factors might have been at fault. 

Sorry the picture didn't show up. I had cut/past into the body of the post. Anyway, the three panels were between two layers of peel ply with a common vacuum bag and common flow media. The 6 oz twill was in the middle between the two heavier panels with about an inch gap between all of the panels. All three panels were infused at the same time with spiral wrap ontop of the flow media along the bottom edges and a breather along the opposite edges to the vacuum source. Flow pattern was normal.

It seems your tow is the problem. I tried unidirectional carbon once. It didn't infuse at all. It was in the middle of a twill stack and the tow acted like it was a sheet of plastic. It just stopped dead. Make real sure your mold and the resin is nice and warm. A thick viscosity can really mess things up I have found through experience.

Fred