On the B757 with RR engines, you need two hoses to start the engines properly. We have a big airstarter with two hoses and that is just fine. Using a single hose airstart unit you are asking for a hot start.
However, in ARN T2 there is a built in airstart system in the gates. It consists of a enormous tank underground pressurised to 40psi. A SINGLE hose comes out the ground, and can start a B757, and a B767 quite adequately. There is enormous mass flow down the one hose. Apart from this I have never started a RB211 on a single hose.
Positioning of the starter really depends on the gate and jetty arrangement. We try and park the airstarter in front of the wing and away from the jetty (very noisy). It is usually quite difficult to achieve easily on any Boeing or Airbus. The DC8 and DC9 are much easier as the connections are not hidden away under the centre fuselage.