We have understood from this question that you are referring to a situation where the margin between two or more bidders’ final scores is very small and that, according to a stated moderation process, this “triggers” a moderation of the scores.
The PCRs do not prescribe how the moderation process should work, only that whatever moderation is carried out is done so in a way which is transparent, non-discriminatory and treats all bidders equally. It would be important to stick to whatever moderation process you had originally set out in the procurement documents.
It would in theory be possible to state in your moderation process that, where the margin between two or more scores is very small (using whatever % the authority felt appropriate), that the moderation would be triggered and the scores would be looked at again to ensure confidence. However, this would need to be recorded and, where scores were revised meaning a change in identity of the winning tenderer, this is clearly a risk for a challenge from the newly disappointed bidder.