Don't get me wrong, I understand you want to protect your efforts. But, AGPL is there to allow developers insight and transparency in other implementations (forks). This also means that nothing limits you to merge these changes back into the original main branch.
This accelerates innovation by forcing a level playing field. The only advantage is the first mover's you hold, the merit of features and the goodwill of the community. You might have lost some of the latter.