Base timing is set by the crank and camshaft sensors.
They are not adjustable.
Base timing is well in advance of max advance since the computer can only delay timing, not advance it.
Ignition timing is calculated from "maps" burnt into the chip. Further delay of timing is learned if the knock sensor causes retarded timing on a regular basis.
The only way to change timing is to affect the internal "base" timing delay within the computer or as Kremit said, get a new chip.
