What are the values of Average Power Phase in the .FIT file?
Looking at the ANT+ Power profile from this page.  'Power phase' and 'power phase peak' are different.
'Power phase' is where the positive contribution starts and ends.
'Power phase peak' are the start and end of peak power is being produced.  Peak power is potentially a configurable amount but defaults to 50% of the total power.
Angles are measured clockwise from vertical.

The 4 number you have are Start angle, End angle, Arc length and Center.  This is from looking at the FIT SDK.  The arc length and center look sensible given your numbers.