..........if i'm understainding correctly lito.sf, you're wanting to mask a miniscule area on a compound curve ?????.........
my
......art supply &/or drafting supply stores sell
chart tape......a very very very narrow tape product, relatively inexpensive, with sufficient adhesive for modelling projects.....
point being.......the narrow tape will form easier around complex surfaces........
or
give Tamiya tape a try.......it's quite thin.......and cuts like a dream and you could make your narrow strips from it...........
hope this serves your purpose