Hey, those constructions look great! It seems like you are looking for the correct cues on the head and face for these constructions, so the only advice I can give you regarding this exercise, is keep doing it regularly. There are some other 2 tips I would give you. You mention that you did some minor revisions on some of these at the end of the session, if it was just to add a little bit of detail so it captures the portrait better, that's fine, If you had to reconstruct some part of the head so it looked more proportioned, do so wisely and not so often, it may become a habit that turn time sessions kind of pointless if you don't respect the time limit (just something to keep in mind, since it happened to me! xd). Secondly, you may want to add to your pool of exercises some head gesture drawing, when focusing too much on the loomis head it's kind of difficult to deviate from the formula, so you can be more fuid and expressive with the drawing. For applying gesture to the head I recommend Steve Huston (there's a 3 hr youtube video on the New masters's academy channel where he does some demonstrations). You are on your way, keep practicing and experimenting!