There is a second trap with the RLV11. System probe for the
extended bus address register to tell if it's a RLV11 or RLV21.
IF you have a device right after the RLV11, the probe is fine
and the system aassumes a RLV21.

A second ball of hair is the J-11. If you have a full 4Mb, you can
address the last 8K as instruction without frobbing BSS7. Only
D-space references assert BSS7, or sould I say, only references
reloceated by D-space PAR/PDRs assert BSS7. This is usefull,
a it give you another 4kw of instuctions for your driver!
Does nothing for data or poll space alas.