Intruder,
Just like the Flaps 10° to Clean transition, there is also a 'crossover' point for the obstacle clearance advantages when considering Flaps 10° Vs Flaps 20°. Near in, Flaps 20° gives the best runway and obstacle performance, after the 'crossover' point, Flaps 10°, at the expense of poorer runway performance, offers the best obstacle clearance.
Regards,
Old Smokey