I like how solid your forms feel, they have nice overlap and perspective. It looks like you might be lengthening the back plane of the jaw, which makes it look longer compared to the cranium; could be why the heads feel narrow?

Hi, Paul, I may have some tips that can help. First, the hair here looks really nice! But I think that when focusing on studying the structure of the head it's better to remove it altogether. This way you're forcing yourself to think about the structure of the skull, and avoiding distractions. It might be helpful to think of the face as a landscape whose features form protrusions and depressions which will overlap as the head moves. For example, generally in 3/4 view, the protrusion of the bridge of the nose blocks the inner corner of the far eye, which is set within the depression of the eye socket; it looks like in some of your drawings you're pulling that far eye out a bit, which is flattening the skull. Finally, it looks to me like you're using symbols when drawing the features. Generally our goal when drawing is to represent the edges of 3D forms (which can be done with lines, value changes, etc.). Lines don't actually exist in the real world, they're just a tool we use to describe the thing we're drawing, so always be thinking about the form you're trying to represent when making a mark. It looks like you're already thinking a bit about this with the core shadow on the nose, so keep that up! For all the features, though, I think it would help you to break them down to their simplest geometric shapes first (spheres for eyes, cylinders for lips, etc), which can help divorce you a bit from the symbols that tend to be the first things that come into our mind when we think of these objects. Simpler forms are also easier to turn in perspective, so this also makes approaching different head angles a bit easier and more methodical. As you add details to these forms, keep in mind the anatomical function of that feature. For example, the eye must be spherical to move in its socket, so be sure to preserve that sense of roundness when you wrap on the lids. This got a bit disorganized, but I hope there's something of value in here. Good luck!