Hmm indeed, SYS:Storage/DOSDrivers/ is the only location that actually uses SYS:. I never actually realized this before...
Everything else uses the assigns, for example FONTS:, DEVS:, LOCALE:, KEYMAPS:, PRINTERS:, HELP:, LIBS:, L:, S: and C:
So basically what you need to do is:
Assign FONTS: Somewhere:else/my/Fonts ADD
Assign C: Somewhere:else/my/C ADD
Assign DEVS: Somewhere:else/my/Devs ADD
Assign LIBS: Somewhere:else/my/Libs ADD
Assign LOCALE: Somewhere:else/my/Locale ADD
Assign HELP: Somewhere:else/my/Locale/Help ADD
Assign L: Somewhere:else/my/L ADD
Assign KEYMAPS: Somewhere:else/my/Devs/Keymaps ADD
Assign PRINTERS: Somewhere:else/my/Devs/Printers ADD
Assign S: Somewhere:else/my/S ADD
*and*
If you want C:Mount to find Somewhere:else/my/Storage/DOSDrivers/ aswell, then:
Assign SYS: Somewhere:else/my/ ADD
