XML deltas

Hello,

is it right that incremental dumps of XML files with deltas can become
bigger than incremental dumps (or full dumps) without deltas? I think
it's possible if more than half of the file is going to be deleted in
the new revision.

Does anyone know of any studies how some XML delta algorithms (maybe
also compressed) compare to bzip2 or 7zip compressed XML incremental
dumps (without deltas) in resulting space consumption?

greetings,
Johannes