The male plug should have a .1 inch start depth. If you start on top the male plug will just start in female pocket. You may think this is counter intutive but it works. The reason it works is the male plug must be slightly smaller than the female pocket. You want a small gap at the bottom of the female pocket to give glue a place to go. The male plug ahould not bottom out in the female pocket.
Depending on your female pocket depth you may need to increase/decrease the start depth of the male plug.
See my post oak and cherry inlay.Vcarve Inlay Oak and Cherry - #15 by gdon_2003