Not sure what you are referring to ACT.... The circumstances of tobi's panel is the exact same as shisui's when both are almost the exact same height... having itachi come up to the bottom of their neck's...
Panels...
Shisui's... only a couple feet apart from itachi (shown in the next panel from a different point of view...) and clearly on level ground, just draw a line....
http://www.mangakong.com/manga/Naruto/590/10
Tobi's... only a about a foot apart, but still not that much further apart then shisui was from itachi... on leveled ground as well...
http://www.mangakong.com/manga/Naruto/590/16
ANd in case you are blind and need a way to determine and compare, I drew a line for everyone...