Difference in 1.4.10 Testing Approach

I hope all is well. I'm finding that different groups test 1.4.10 Reflow using different methods:

  1.  Set width to 1280 px (for vertically scrolling content), zoom to 400% and test
  2.  Change the viewport to 320px without adjusting zoom and test

In my experience, the results are different. What may create issues with a loss of content using option 1 are not issues when testing using option 2. Are both options acceptable for testing reflow? Does option 1 catch a larger subset of potential issues?

Thank you!

Justin