brat,my rocky(
my boy)was exactly the same.even looked like your brat
he however went further and attacked me,if i interfeared when he saw another cat outside,he also sprayed.
i had 2 feliway plugins and they actually worked to calm him down.
we went as far as blocking access to our deck for strange cats and put heavy wooden patio-door blinds to block rockys view.
in later years this behavior stopped,i don't know if it had anything to do with it,but he was on meds for hypertyroidism and this behavior stopped.he always was a very loving,very smart kitty,except for his panic-attacks seeing a strange cat outside.
i also had 3 cats,since rocky passed at 14yrs old(thyroid-cancer)i now only have 2.