The only way i got it working was to make it gmax ,this was the full runway ,i managed in fs9 nearly a 45 deg sloping harden ,after that it doesn't work and you would fall through it ,plus what a angle to land on anyway ,
after my findings in fS9 i moved on to trying them in FSX like this tread i made here with a fun tester ..
http://nzff.org/forum/viewtopic.php?t=5809