Reverse cooling

I am asking this question mainly because I have my engine hooked up for reverse cooling. To get it all burped. I have jacked up the front end, left and right side. Did this twice. The motor stays cool with pump on, but for some reason will still puke water into catch can. I have an 19-21lb stant racing cap. I have pressured the system to 18lbs without the car running. Holds pressure all day long. But like I noted with car running water gets past the cap. So I was thinking maybe it has something to do with reverse cooling. 20200331_161222.jpg