I raised this topic at an EASA meeting nearly 3 years ago at which the participants agreed that the wording was ambiguous:
Outcome: The participants agreed that the 25% rule should be based on the minimum hours established in the ATO course approval. However, this issue should be reviewed by the GA task on simplifying the balloon requirements to further clarify the intent. This task is already considering changing the 25% requirement to 50%.
Post-meeting note: As the RMT.0654 on balloon licencing requirements has been, postponed until further notice, EASA will include this issue in RMT.0596 updating examiner requirements.
But RMT.0596 has now been absorbed into RMT.0194, with no NPA expected until 2020 - and no Decision before 2023....
Unofficially, the CAA advised me to tell people to use the 25% of minimum course requirements figure (i.e. 6.25 for the PPL(A)), but if more was needed than a note of explanation should be included with the application - for example, an FI went sick on the day and the only other person available was the FE who later did the Skill Test.