RDSK block values are mostly irrelevant, only used by partitioning tools (but obvious bugs fixed).
Not using minblocksize is by design. I am quite sure there are drivers that expect 512 and nothing else, especially when looking for LSEG blocks. Even if filesystem uses 256 byte blocks.
This feature is designed to be safe with normal HD use case, not to be flexible with weird things that no on else will ever use
