Issue 5 of CAO 20.7.1B seems to have tried to shed a little more light on the regulatory requirements of Obstacle Clearance Requirements, over and above that required for the Takeoff Climb Requirements.
12 OBSTACLE CLEARANCE REQUIREMENTS
12.1 For the purposes of subparagraph 4.1 (ba), the take-off obstacle clearance requirements are met if the net flight path of the aeroplane, following failure of the critical engine so that it is recognised at V1 appropriate to a dry runway, would clear by at least 35 feet vertically all obstacles in the take-off area.
No issues with that.
12.3.1 For paragraph 12.1, an obstacle-clear take-off gradient, for a runway and a direction, published in Aeronautical Information Publications, may be used for the part of the take-off area commencing at the end of the take-off distance available and extending for the length of the surveyed area on which the gradient is based, despite the fact that the rate of divergence of the surveyed area may be less than 0.125D and that the length of the inner edge of the surveyed area may be less than 300 feet.
That's what I'm trying to use.
12.3.2 The requirements mentioned in paragraph 12.1 are met for a part of the takeoff area if the gradient of the net flight path in that part is not less than the obstacle-clear take-off gradient.
OK - this says that segment 1 MUST be considered as part of the obstacle clearance requirements.
So this brings me back to whether the factors given are an accurate way of moving the end of the 1st segment back to over the runway.