Mine is butted up against the heatsink without the cuts in the bar and it's fine, no difference in temp and I can feel the air being pushed up at the end. If you don't want to cover the fins with the bars in the center you can either run the angle aluminum perpendicular to the heatsinks and cradle it that way, or cut off two pieces and bolt each one to the interior of the heatsinks and then run your angle across the center.
The first option is easier and allows for you to move and/or add more. The second option is more permanent as you have to bolt two pieces to the heatsinks and you won't be able to readily add more in the future.