If you move your router to the middle of the waste board halves, lower the Z till it almost touches, then give the waste board a firm press down, you will see the gap between the end mill and waste board open up without much pressure. On mine I could see it in the cuts I was making, the flex towards the center was making cuts towards the front deeper than in the center. What I did was replaced the two piece MDF waste board with one piece of MDF, then I took the leveling feet off completely and rested the whole thing on a rubber matt. After that I shimmed up any spaces in the front and back of the end plates with some thin MDF shims, and trammed it flat. The way the leveling feet support the ends in combination with the 2 piece waste board and no support in the middle is what causes the deflection/sag. The end plate angles are more robust than the shallower folds of the cross brace sheet metal simply because of their geometry, and a non solid waste board, you get sag. I thought about about adding some sort of leveling feet to the middle, but in the end it was simpler to just remove them completely and let my bench support it all of the way around.