From looking at the pics on
amiga.resource.cx...
Like many old SCSI controllers, on-board passive termination is hard-wired and cannot be disabled by a jumper. There are three resistor packs next to the SCSI connector. If you wanted to remove termination you need to desolder them. (If all else fails you could try doing that and use an internal active terminator.) Edit to add: the resistor packs may be socketed on the Fastlane board, in which case you could remove them easily.
What you can change by jumper is whether the Fastlane supplies termination power to the SCSI bus.
Looking at the jumper settings, you could try disabling synchronous transfers by opening jumper 4. And try closing jumper 3 to enable "slow cable mode".