These inquiries would be answered in The Vinyll Engine forum. They are dedicated to Vinyll and have lots of tutorials and such that go into depth on each topic. I only mention it because they have been a great help to me on some of this stuff. To answer your question the grooves do narrow and the angle becomes more acute resulting in greater side thrust on the inside groove. The old issues of the Tracking Angle magazine had a 20 page white paper on bias settings for tonearms. I believe it is still available as a download on the net. Free of course. I know they took before and after electron microscope photos of the groove of a record to show the effects of this.