Well done ws. You did exactly the right thing.
WAP can be an awkward one to find, in as much as the Chilterns can give you the option of seeing what you want to see if you're too far east, as you found out. Don't forget, Princes Risborough has the railway lines running through it. Also, head west and you could pick up the M40. That will lead you to south towards Stokenchurch mast (and the threshold if you're desperate!!!) but be aware of the gliding site at Haddenham, the jumpers at Lewknor and of course Benson MATZ.