Sorry
To be specific about this
The one meg chip mod should be on the A500 motherboard itself near the 68000, jumper 2
https://www.amibay.com/threads/a500-r6a-1mb-chip-ram-modification-caution-dialup-users-excessive-h-w-pr0n.4984/This allows 0.5 the regular slow memory to be to added to the 0.5 meg on board to get 1 meg chip.
up to $0FFFFF
http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node00D3.htmlAs for the gary adapter, I am wondering if it allowing some of the trap door ram to added to the 8 meg auto config space
ie $200000 - 9FFFFF 8 MB Auto-config space
you could check this with sysinfo or another utility.
FYI slow-fast ram is usually mapped at $C00000
It might be useful to look your ram mapping.
Regular Fast Ram (ie the GVP HD8 ram goes to the 8 MB auto-config space)
I have an GVP HD8 on my main A500, and an IDE Ad540 on one of my other A500s (which is a large trapdoor memory expansion with a gary mod plug in)
However your trapdoor expansion might be different which is why I would look at the address space with sysinfo