In a forest retreat turn ambusher on (S) -> (s) so you can see vision arcs, and then like Shonai_Dweller mentioned (l)ook, then < to move up z-levels, if you see someone's arc.
(https://i.imgur.com/rpjcuPl.png)
(https://i.imgur.com/l6kTeq5.png)
(https://i.imgur.com/W1Zn4u6.png)