This decision results in a performance penalty whereby, you end up over the screen (in the worst case scenario) crossing the as low but NOT LOWER THAN 15' agl. However you still must reach the safety speed V2 by 35'(by law).
Interesting, but could you please supply the appropriate FAR to back this up!
My understanding is that you reach V2 at 15 feet and thereby your Net Obstacle Clearance is 15 feet, at no time do you revert back to 35 feet clearance!
extremeP, Credit for 3 engine aircraft = 2 engines, 4 engine aircraft = 2 engines on opposite sides.
Its worth noting that some manufacturers produce their data based upon ZERO thrust reverse for twin engine aircraft. Boeing provides both 1 engine reverse and Zero engine reverse for the 777.
Mutt