Sorry if this is the long way around, but I think it will help explain better what you are seeing. The compression and exhaust strokes look very close to the same at the beginning. The following is actually instructions for a valve adjust, but should sow you the difference.
Split the firing order in half:
1 5 3
6 2 4
These vertical pairs are "companion" cylinders, both at the top at the same time, but 360 degrees out of phase with each other. When #6 cylinder has the exhaust valve closing, and the intake valve slightly open, #1 is ready for adjustment.
Hope this helps, I'm sure there will be others.
Larry
