Actually if the TPS IDL-E2 setting is off (i.e. > 2300 ohms with throttle closed) then the timing jumper will have no effect on the base timing:
- http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml#Troubleshooting

In that case, 12 BTDC is close to factory timing (i.e. 12 BTDC w/o jumper = 5 BTDC w/ jumper).