Assuming correct alignment, inner groove distortion is generally the result of:
1. Resonance and improper tonearm damping.
2. Reduced groove velocity at the inner grooves. On a record the average outer groove starts at 11.5 inches diameter and the inner groove at 5.8 diameter. So, the inner groove is 50.4 percent the linear velocity of the outer groove. Put another way, if someone handed you a record that ran at 16.8rpm you wouldn't you expect the outer groove to sound great. That's the effective velocity of the inner groove if it were to run at the outer part of a record spinning at 16.8 rpm.