There is no strategy to position oneself for an UG except: (1) buy a first class ticket; (2) become a higher level of medallion or (3) buy a higher fare class ticket. Not having a seat assignment won't help you. Ask the SC agent to help you assign a seat. If that won't work, get to the gate early and tell them I they clear any UGs to try to put you into EC, aisle, whatever you are seeking. You might be stuck though.