Perhaps I am not getting the true picture of this but the "spot of gray paint" seems to imply you can see the side of the enclosure, just not the switch handle. If a person standing in front of this switch was in full view, I would say it was within sight. Another issue might be, can you approach this from the other side? (someone walk up and flip the switch without seeing you working or you seeing them).
If you are buried in the tub enclosure working on something, nothing is actually within sight.
The only 99% safe way is LOTO but you still have the 1% idiot out there so nothing is 100%