How can I get a better flush?

Villeroy and Boch (again). Low level cistern fitted with new Dudley Turbo 33 syphon. When flushed the water NEVER goes completely round the rim (it never did), and I suspect this may be why it requires up to five flushes to clear. How can the pressure/flow be increased to give a strong flush? Do you remember those wonderful high level cisterns with a pull chain which worked first time every time? Is the pursuit of fashion really progress?