EIP_OBJECT_AS_REGISTER_REQ checks for maximum assembly size are off and documentation needs clarification

EIP_OBJECT_AS_REGISTER_REQ (0x01A0C) is not rejected cleanly when parameter ulSize is in range [504 .. 516]:

he maximum size for the assembly is 504 bytes. There can be additional 12 bytes of meta data for the mapping of RUN/IDLE, SEQCNT and PRODFLAGS.

I have noticed that the checks are unclean a few days ago.
It should rather be [504 .. 516].
We should improve the maximum size check in the code, maybe depend it on the actual MAP flags provided. In the documentation, 504 is correct if no map flags are given and 504 + 4 + 4 + 4 if all three MAP flags are given.  Emphasize that 504 bytes is the maximum size of the actual assembly.