Hello and welcome! The various head angles are a good practice, I keep on having trouble with top down myself, even though I'm 6'4" so that's the angle that I wind up looking at most people from anyways.
Good stuff, I look forward to seeing the H2D stuff too, those are great books.
Yeah drawing the head, or anything for that matter, from an extreme angle of up or down is quite daunting. It wears me out mentally quite fast. It all become easy for once I actually went through the intro chapters of H2D and ModernDayJames' gumroad video on dynamic drawing.
I used to hate perspective drawing, always thought it was too technical. I mustered up the courage to go through the first and second chapter of H2D and I have to admit, I'm loving it. But at the moment, I'm focused on anatomy but understanding the concept of perspective and being able to breakdown everything to simple 3D shapes really helped drawing these. I'll be uploading some work at the end of the week (I'm thinking this should be a weekly thing, to keep myself studying consistently. Thank you for taking the time to comment! 
NOTE: I have already done similar sketches for the skull and rib cage. This is what follows from that, drawing the shoulder bones and arm bones.
A couple of things to note of what my mindset is when I'm doing these drawings:
Then I'll follow up with the pelvis and leg bones. I'll probably leave out hands and feet last, as they are probably the hardest to draw and also my weakest points.
A couple of sketches I did about studying the spine and its relation to the skull, ribcage and pelvis. 
Spent the entirety of the last week continuing with anatomy by practicing the pelvis. The first 2 drawings were drawn as explained by Proko, but I felt as though it was little too simple. From the 3rd to 5th are the from Stephen Rogers Peck's book of Anatomy and how he explained (very detail oriented while breaking down the landmarks and points of consideration). All of these starting from the 6th are drawn on top of reference models, with a mix of male and female. It became pretty clear after a while, you really don't need to know all the details but instead knowing where the landmarks and the variations in the genders were good enough. I think I definitely went overboard with trying to nail certain details.
12 days later
Instead of trying to draw as many dynamic poses as possible, I thought I'd take a crack at drawing the default pose using Marc's anatomy proportions layout. Its basically the same as the Loomis method, except I prefer the Cranial by Robert Beverly Hale.
You can definitely notice my lack practice when it comes to muscle anatomy especially in the abdomen area. Having watched Rey Busto's class on anatomy, I'm familiar with where the origin/insertion points are and what are the general shapes of the muscles. The most difficult area to nail was at the point where the Serratus, Obliques, Lats and Pecs overlap. I should definitely do more drawings that is specific to my weaker muscle points instead of sketching whole poses.
Another of my mistakes (or lack of awareness), was correct scaling and by that I mean when I first sketched the male figure, the body overall was very narrow. This probably due to the fact I've gotten a lot more comfortable drawing female than male anatomy, and subconsciously sticking to the proportions of drawing the female figure (example: the ribcage is two cranial units wide, but in the male its usually 2 and half cranial units, to account for the wider thoracic arch). In this case however went with one and half cranial units wide for the female and two cranial units wide for the male. There's definitely a lot more I learned from this, but I don't want to drag this out for too long.
1 month later
Its been a while since I posted here. I took a month's break travelling back home. Taking a break was something I didn't realize that I needed but it helped me reflect on the work that I was doing and how I need to slightly shift my direction. I was gone for the month of August and here are some of the drawings I did in July (it was quite the slow month, thus the need for a change). I feel as though doing these gesture/figure drawings didn't really help in as many ways as I would have liked it to. I was expecting it to help me understand anatomy and its motions, but instead I think I need to focus on separate muscle groups as I find myself often going back to the anatomy resources or even forgetting things that I haven't learned because I haven't put enough time focusing on different anatomical parts.
Value/Portrait study. I often get distracted from completing a painting when I get lost in trying to recreate the reference as it should be. This was a painting I started last year but gave up halfway through as I found the overhead lighting rather difficult AT THE TIME. I came back to this a month ago and was able to finish it up without much difficulty. I think I could have done more with rendering the hair, add highlights and give it better form. Rendering hair (especially short and messy) is definitely one of my weakest points.
9 days later
Another portrait drawing. At this point my goals here are values and rendering. I think the complexity of facial features make for a great exercise in practicing rendering form. Obviously it is important that you are able to breakdown the forms into simple 3D shapes when in the drawing phase, which for some reason I still prefer doing traditionally. Surprisingly one of the hardest features to render for me is the nose. 
I really like how confident your lines appear to be. Big fan of your studies esp. the pelvis ones. Super crispy and inspires me to do more studies.
