Hello,
It is always advised to use RUTX50 with all four antennas attached for the best performance. Besides, technical details can get confusing for many users and antenna arrangements become relevant in more elaborate cases such as yours.
I will, of course, address your suggestion for consideration.
Regarding your setup, based on the picture you have provided, I would suggest to place antenna 4 above antenna 2, as antennas 1 and 4 (I assume they correspond to most left and right ports on the router) are used for transmission, thus placing them higher, would provide a better line of sight as well as better coverage.
Best regards,