LXPanel takes far too much space for its strut, if the primary monitor is not the largest monitor on the system, and the panel is at the bottom of right of the monitor. As an example, with a 1920x1080 monitor as the primary, and a 3840x2160 monitor as the secondary, and a bottom aligned panel ono the primary monitor of 26 pixels in height, the requested strut size is 2134 pixels. Openbox's validation will trim this to 540 pixels, but the result is that maximised windows only take up the top half of the screen, and new windows for some apps will be very small, vertically.
A patch is included with this report.