Your issue is a common one that I have seen in various fits. It was even a specific topic taught in the Body Geometry program during my original fit training. The knock out of the legs is called a “wood-chop” and the belly is a common cause for it.
Not much to do other than keep the upper body up or lose the belly. If you can live with the wood-chop, you can go as low as your are comfortable, but be cautious about possible pain on the hips and knees. That extra lateral motion can lead to repetitive stress injuries.
Maybe you can snap a pick or get the model of the aerobars and someone can help find what options you have?