Nice Kaneda rik

yeah that can work, but to clarify it doesn't really matter the resolution, just have the full reference image visible, if you have a larger canvas just zoom out of your canvas and just capture the broad strokes with a large brush, set a timer and try capturing as much as you can in the time, a technique is to gauge what the most utilized color in the piece is and lay that down as the base color, then build up the form and composition from there, never laser focus on any one area just work the entire thumbnail, once you lay in the basis and adjust it sufficiently then if you feel there is far more to capture and you have time half your brush size and do another pass. there are countless ways to do studies but i find that type of time focused session can help with your observation.
Value studies would be taking a piece and desaturating it and then reproducing it with the same method strictly in greyscale so you don't overwhelm yourself with the colors, other exercises are less about the composition accuracy and values per say as it is about recreating the colors by eye alone.then you can always do some eyedropper comparison afterward to see how close you were, with paintings. if you haven't been acquainted with the science and art of light and colour you'll be surprised how relative colors really are, ie grey looking blue in a warm scene and conversely looking a dull warm orange in a cool scene.
I rather like yours better, I'd probably go more top down.

some more render tests, marmoset Toolbag, sub-dermis/heat maps for subsurface work well



just did a quick 25 minute one to give an example.

a point to be made is to pick and choose what to concentrate on, even adapt, in this one i started with an A4 divided into 3, (so i could do 3 seperate studies on the same canvas), resulting in a more vertically compressed panel than the source image, I realized this, so i set a task to myself to compress the composition to this ratio, Also if any details of the source image are not to your taste or liking, or you take issue with it in some way, then you are free to just omit it, or if something like the deer is not important to the intent of your study then feel free to omit them too, just make sure that you are paying attention to the relationship of colors and values, warm and cool, light and shadow as you go
a while afterward you will start to notice the discrepancies easier. and if you wish polishing it further can be a worthwhile task. one of the big things about many artists that people forget is they use reference strongly and some artists take months to finish a piece. so you look at Frazetta's work and he had live models and photos, he did sketch sessions with models, and took photos in pose, and he'd take a long time on his paintings.
and artists took their lifetimes finding and honing their techniques, so learning from all that work and experience can be really potent.
progress every 8 minutes or so

just a screenshot to clarify the configuration
here. 33% zoom, but you get the idea of the screen space.
is it perfect? no far from it, but for 25 minutes you can be pleased enough for what you manage to accomplish, taking an hour or several hours you can go more in depth and study the details of a painting. but decide atleast vaguely what you want to capture and "study" whether it's predominantly color, or composition, or detailing/rendering techniques. and focus on that, this one was mostly about color and comp.
having two monitors with different gamuts doesn't help, I recently upgraded i now have 2 27" LCDs my latest an IPS (in plane shifting) the color on this one is fantastic

the older monitor the ref was on not so much.
P.S i'm really tired so if any of this is inarticulate nonsense my apologies