We have passed your question on to the Chief Referee for the Tournament and will post his reply in due course.
There is no specific answer to this question but firstly, the NZBSA has no input into how rules are interpretated.
All referees worldwide follow the rules written in the IBSF Rulebook. As for guidelines it is clearly stated in the first sentence of Section 3 Rule 14 Foul and a Miss "The striker shall to the best of his ability endeavour to hit the ball on. If the referee considers the rule to be infringed he shall call Foul and a Miss.
Many points must be assessed by the referee, with the upermost being the ability of the player and the difficulty of the stroke being played. As this is a judgement call by the referee the decision is his alone.
No two referees are going to see any particular stroke played in the same light. It is better for a referee to be consistent within the match regardless on whether his calls are considered harsh or not. Hopefully the decisions made by the more experienced referees will offer more consistency.