I never played there sadly, but can't you just jj straight up, fire, and then come back down and wait untill you PPC recharges?
Much better than staying in the open IMO
There's about a second of hang that makes you easy prey to just about any one. Giving some sideward motion to the jump helps, but you throw off your aim and risk jumping off the building.
As for being out in the open, consider that most of your shots are going to be at an angle, so you can duck out of sight by merely moving back along the roof. Using your instant-response feet compared to sloppy jump-jet mechanics (not that I ask for anything better, they're jump jets) is always preferable to me.
I'm not even too sure the current walls really conceal you, as they come to about chest level. I'm fairly certain your SRM pods could be hit, still killing you. Ironically, making the border taller than the battle armor would allow them to collide and latch on with the average jump, allowing the battle armor to walk freely along it.
I find that a bit silly, though, and I think we could just reduce those little walls to about thigh-level on a battle armor.