This wasn’t my experience and maybe I’m misunderstanding what you mean. If your foreign sourced income is below 6.7 million it means you aren’t subject to the AMT, but it doesn’t necessarily mean that you pay no taxes. The AMT calculation simply kicks in at that point and you pay the higher of the two between the AMT and standard calculations. Here’s the passage from page 67 of the document you linked:
“Resident taxpayers with AMT taxable income of more than NT$6.7 million may be subject to AMT at the current rate of 20%. Under the Income Basic Tax Act, a taxpayer must calculate the amount of AMT due on income subject to AMT and compare the result with the regular income tax payable. Resident taxpayers must pay the higher of the AMT or regular income tax payable amounts. Any foreign taxes paid on offshore income may be offset against AMT payable with certain limitations.”
As always, best to consult an accountant.