Great review! I’m a bit lost with the size of that pochade box medium. Is the 8x11 inch the outer size of the box or the metallic holders inside the box? Thank you!!
It's a bit late to be replying, but 8.4"X11.25" is the size of the box itself. New Wave says the maximum vertical height of panel to put on there is 10 inches. You can buy a separate extension bar that allows larger panel sizes.
I just got the U Go tripod, it's lovely and compact for carrying, but feel it's a bit short and I'm hesitant to extend the centre column fully as you have - do you find it compromises the stability?
With any tripod, stability starts with the legs. Extend them first if there's enough room. With the center post, make sure the clamps are tight enough. There are going to be situations with any field easel where it's necessary to keep it a little shorter- high winds and soft ground are always a challenge!