How can I fix lack of water for flushing. ?

I purchased a Perdita toilet with Jolly Tank cistern from B&Q as part of a full bathroom suite. It was impossible to achieve the 555mm height above floor level for base of cistern for 2 reasons. The vanity unit was not high enough internally and the right angle pipe supplied to fit between toilet and cistern base had insufficient vertical height thus limiting max height achieved to 500mm approx. Cistern tank fills to max but insufficient water flow to clear waste on long flush. All other fittings as per instructions. Any possible solutions welcomed.