Problems with multiple camera viewports

I’m embedding a JME canvas in a swing application. I need two views, one from each camera. I’d like them to be next to each other horizontally x: (0-0.5) and (0.5,1), y: (0,1) and (0,1). I’ve used the Application’s cam for the first view and it worked fine while it was taking full space of the canvas. After splitting into two, it became distorted. The documentation says it’s because the aspect ratio differs from the window aspect ratio: “In these cases, you must recreate (not clone) the ViewPort’s cam object with the right aspect ratio. For example: Camera cam5 = new Camera(100,100);”. What would be “the RIGHT aspect ratio” ? Do my viewports have to keep the window AR ? If so, then I can’t just split my canvas horizontally. As far as I know I can’t make two canvases, and as I’ve read in other threads it’s recommended to just create multiple viewports, and I did. I just get terrible flickering, like the canvas isn’t updating.

Before posting big block of code, which is mostly copy paste from the multiple camera views tutorial plus disabling the mainview of the default camera, any suggestion would help.

Thanks in advance