That ridge comes from pooling at the eponychium, but it's not just a matter of thinner coats, but of placing the polish properly. This is an old fingernail fixer video, but it still gives a good idea of good technique - ,
The part about placing the brush in the middle of the nail and pushing ("scrubbing") is critical. i believe it was Gigi Rouse always talked about making your base coat so thin that you could run the edge of your nail over it and not feel any line of demarcation.