Should I join the evaluation phase if I am not part of the top-performing teams on the validation leaderboard?

YES, you should.

One of the main objective of challenges is to benchmark different approaches. Therefore, if you have developed a technique that didn't reach a very high level of performance, we strongly advise you to join the validation phase because: 1. The community needs to know which approach is underperforming. It helps to give insights for future work. 2. Your approach should be presented in the joint manuscript that will be submitted after the challenge. 3. The first co-author(s) and the last author of the short papers will be qualified to be authors on the joint manuscript. 4. Your work should be rewarded with a publication. All challenge participants will have the opportunity to publish their methods as part of the BrainLes proceedings.

Reuben