I have seen on luckchain forum that some with a lower rank are eager to participate. There who made himself a signature by editing what we have now and made simple one for himself. Yet, he seemed not accepted I guess. We have many junior members on BCT who can carry and promote luckchain.

This means by just few revisions on current design we can make one for junior.  So adjusting structure for senior and above can be but not necessarily. As I see on rules, you like to distribute signature bounty equally by activity but regardless of ranks. Sig design for Full members are suitable for above ranks also. I made simple editing for junior and senior (Hero too). You may have it, pls. check PM. Otherwise, if you like new design, the one suggested by sir @electronicash who's expert at it is a good choice.