The constant aspect approach commences at Low Key, which is typically, Downwind with the aft end of the wing tip on the Initial Aiming Point. The height at Low Key is aircraft dependant.
Having established the vertical angle between your sight line to the IAP and the ground, maintain this angle constant around the base turn regulating it with the bank angle, ie increasing bank angle as you turn into wind. If the angle steepens turn away, if it shallows turn towards. Roll out on final at about 500ft, then take flap to bring aiming point towards you.
High Key is typically Low Key + 1000ft Upwind on the opposite side of the field (Deadside). Fly a curve from High Key to Low Key then continue to IAP. In doing so you will pass through the 1000ft point.