Sonic Boom does not occur at Mach 1

[broderbund67]

Hi,

I did a flight at 20,000ft, wind 284-062. Flying hdg 325 the sonic boom occurs at M1.05. Flying hdg 159 it occurs at M0.93.

I would expect the sound effect to happen at M1.0?

See attached track.

Thanks

Sound bar.trk