Actually, just for the sake of reference to the OP of that pic. That wasn't a picture of the jig I built. Just one I found on the web that looked similar.
I went a bit nuts and had the bottom brace adjustable via two bolts through slots in a bottom piece of MDF. Just in case I ever wanted to use different sized crown modling with it.
Of course I never did so I just wasted time unless another project comes up.
I'm Riffing. People usually stop me when I'm riffing. Or carry on without me. That's also an option.