I still say look out of the window, use the radio where appropriate (listen out, build a picture of traffic but always watch out for the one not calling, for what ever reason, either a non-radio equipped aircraft, or one who forgot to call) and always be flexible and fit into existing circuit traffic because they have right of way. To assume that a join must always be over the upwind numbers, irrespective of traffic climbing in the circuit, is absurd and goes against common sense, as well as the rules.
The climb performance of some aircraft most definitely means they will be at least 1000 feet agl by the time they reach the upwind end even at the shortest of runways.
Consider this, if a mid air collision were to take place, between an aircraft in the circuit or one joining, who would take the blame?