Stop using your ultimate at ground level, if you're going to tell me that the other team is going to advance down pathways at the start of a round looking at the sky trying to find you... I just don't know what to say.
There are only a few outcomes to this:
1.) You're repeating your tactic by going to the same spot (your fault)
2.) You're advancing too far and they saw your ultimate through a wall (your fault)
When you say you "normally camp the objective" that leads me to believe you chose option 1. A solution to this is to hide in the air on a path to the objective rather than at the objective and vary your travel distance each round. When you ambush someone, you do it before they get to their destination, not after.
You are beyond saving with logic. I'm sorry, I'm so, so, sorry.