A high fermentation score means that there is a high level of gas production happening in your digestive system. The key is understanding how this gas production is affecting you by logging your symptoms.
In relation to how the scores are split, a score of 6.0 with a 1:1 hydrogen to methane split would mean a 3.0 score of both hydrogen and methane - which is low for each gas.
As you may be aware from the information within the app, f-scores are categorised as low, medium and high:
Low = 0 - 3.4
Medium = 3.5 - 6.7
High = 6.8 - 10
Some users find that if they have a generally high background methane level, their hydrogen scores seem to have a greater effect on their symptoms.
It is also good to note that for a challenge day, you can proceed with the challenge with an elevated methane level, provided your hydrogen score is low.