I find jumping up on the boundery walls and crouching down to be a very good spot. Usually players can't tell where it's coming from. They'll soon figure it out though. Prolly the best thing you could learn to do as a sniper on Mos Eisley is learning to wall jump and get on buildings you can't normally get on. Like the cantina. There's several ways to get up there. This serves as a good sniping spot because you can take a shot and move a couple steps to get out of the line of fire coming back at you. It's a large roof with contours that allow for quick stepping out of the line of fire (except from the top of the hangar or buildings of the same height or greater).
Even if players (ground targets) know you are up there.. not everyone knows how to get up there and players are usually forced to take another sniping position against you.