Let me get this straight: the 35ft and 15ft are based on a really tight takeoff , zero stop margin and full thrust and no more space right? In all other cases we will cross the obstacle much higher right?
The situation is not quite that pessimistic ...
If there is no engine failure and the aircraft is operated sensibly, heights will exceed the OEI analysis by a significant margin .. ie the normal situation.
For the OEI case, the takeoff analysis looks at a bunch of cases which are calculated ... one of these will be critical and determine the limiting weight .. noting that the AEO case with its factor can be the limiting case.
If OEI TODR case is limiting then the aircraft flight path may approximate the 35'/15' screen height at the end of the TODR (which will be less than or equal to the TODA) .. otherwise, the aircraft can be expected to be somewhat higher.
From this point, the net flight path as calculated has to clear the actual obstacle profile by 35'. The OEI flight path, actually achieved, will exceed the net profile by (at least) the delta between net and gross.
As the takeoff progresses, this delta provides an increasing pad for actual obstacle clearance.