Probably better to ask in a PSOGC community.
Are you playing on a patched gamecube ISO or vanilla? There is a common 'mag reverser' patch somewhere that makes some changes to how it works. The trigger by default has lower priority than another trigger check which causes it to rarely activate (lower priority than the 1/10 HP and PB checks IIRC).
These mags have Reverser as a death trigger and the specified 'boost' is next to it (if no 'boost', the trigger rate is just the mag trigger rate). There's no real name for these, so I'll just use 3 and 4 which are explained here:
https://wiki.pioneer2.net/w/Mags#Additional_trigger_adjustments
The "negative" boost is explained above that link.
- Varaha - 4
- Kama - 4
- Ushasu - 4
- Asparas - 4
- Kumara - 4
- Kaitabha - 4
- Bhirava - 4
- Yaksa - 4
- Sita - 4
- Garuda - 4
- Nandin - 4
- Ribhava - 4
- Soma - 4
- Ila - 4
- Durga - 4
- Naga - 3
- Pitri - 3
- Kabanda - 3
- Ravana - 3
- Marica - 3
- Soniti - Negative
- Preta - Negative
- Naga - 3
- Andhaka - 3
- Bana - 3
- Naraka - 3
- Madhu - 3
- Churel - Negative
- Robochao
- Opa-Opa
- Pian
- Chao
- Chu Chu
- Kapu Kapu
- Angel's Wing
- Devil's Wing
- Elenor
- Sega Saturn
- Dreamcast
- Hamburger
- Panzer's Tail
- Devil's Tail
- Deva
- Rati
- Savitri
- Rukmin
- Pushan
- Diwari
- Sato
- Bhima
- Nidra
I quickly typed up this list after checking the ItemPMT for BB and GC match for the V3 mags. To check the list of mags yourself (note that Soly's PMT Editor has weird names for the trigger boosts 3 and 4)...
Soly has a PMT editor for Gamecube here:
https://www.pioneer2.net/community/threads/solys-stash.1001/
You can get the ItemPMT.prs from your ISO or newserv:
https://github.com/fuzziqersoftware/newserv/tree/master/system/item-tables