I have found HP5 works better at ei 160 in dilute perceptol, although thats probably more to do with my technique peculiarities. I usually dilute to 1:3 to make 600 ml (150ml stock and 450ml water), then use this at 24 degrees with 2 x 120 rolls placed on one plastic reel - my tank will only take 1 reel when extended to the 120 width. Although, on the odd occasion when I develop 1 roll, i still use 600ml to be sure.
I find 1:3 gives a more compensatory effect than 1:2 and the edge effects seems to have the edge on the stronger solution (if you see what I mean!), although develpment times are fairly long.
Have you read Barry Thornton's Elements too? I find this much more useful than the already very good Edge of Darkness.
Hope this helps.