Even with 30 degrees instead of 28 and an angle on the indicator this value seems very high.
When I did my check I did it with the head off, fitted a magnetic stand with flexible arm using an indicator clock to ensure I got a good reading. I then locked the auto advance at fulll advance, set the 5,20 mm piston position and checked that the original ignition marking and it was at approximately 27,5 degree (same at both sides) so I cut a slot at 27,5 (of the same width as the alternator marking) so it would be easy to use with the strobe light. It works fine!
/Per