I don't like counter-intuitive nicknames either.
Poppy and
Posy as a nickname for pretty much anything drive me crazy. Nicknames like those seem too contrived. The only exception for me would be nicknames bestowed by family and friends.
Ron from
Aaron and
Dan from
Aidan are fine, since those two names don't really have commonly used nicknames anyway. Bel or Bell for
Mabel makes enough sense as well.