This spot is very high so people cannot notice your team from the ground. Make sure your clear the area before going in that cliff and refrain yourself from checking outside. Use sound spacialization to get an idea of where the other teams are.

To access this spot, you will need an Octane. Roughly place a Launch Pad where indicated in the screenshot below and super jump: press your jump key right after you hit the Launch Pad and be ready to air control and climb when you hit the cliff. Once you are there, you can lock yourself in the crouched position. Try to have all your team members at the same place so you are less likely to be noticed.