It has nothing to do with holes. Same effect can be seen with ears.  It is facets with their normals pointing away from the direction where you want the clothing to be within a distance under the skin comparable with or less than the length of the edges of cloth facets. Collision objects should normally be convex. Of course on a human shape one has to make compromises and cloth-on-human simulators are tunes to cope, but the less locations where the desired position of the fabric is not clear on facet-vertex level the better.   In my collisin avatars I usually take out all internals and 'spandax' all extremities.