To put a number on my earlier post, with a 0.8% delta between Gross and Net, it is necessary to fly 2500 ft / 762 M horizontally before the 0.8% 'fat' has 'recovered' the 20 ft lost in obstacle clearance. All of this presumes, of course, that you fly the aircraft as well as the test pilot, and achieve the full Gross performance.
2500 ft / 762 M is probably about half of the 1st segment for most 2 engined aircraft, thus, the remarks originally quoted do indeed refer to close-in obstacles.
Regards,
Old Smokey