i wonder if it would be prudent to compare this to the guidelines of UK CS30 and CS31 qualifications, the more relevant in this case being the latter which is related to felling and processing trees of equal or smaller diameter than guide bar length.
these are not criticisms, more observations that the UK taught felling techniques seem have disparity with the USA ones. I shall elaborate
UK spec specifies that 'sinks' or notches etc to you, need only be 20-25% of the tree's diameter in depth in order to provide adequate releif for 9/10 falls.
i have read in american books 1/3 and seen people take much more on videos
back cuts, whether bored or otherwise, should be noticably above the bottom of the sink in level, but NOT more than 25mm
hinges must be at least 10% by diameter, more on very small trees
as for what to use where.
straight tree/tree with no lean - standard technique. 45 degree sink, flat back cut not more than 25mm above
tree with lean in any direction other than that you wish to fell it in - split level
sink as normal. staying on right of tree, cut 2/3 across up to the hinge, leaving a third holding the tree still.
insert wedge or lever into the cut
move around to the other side of the tree and with the saw nose pointed down approx 30-45 degrees, remove the remaining third, undercutting the first cut at which point if done correctly, the tree will sit back on the wedge, lever, whatever. using lever or wedge techniques will now drive the tree over in the desired direction
tree leaning heavily in direction of fell - dogs tooth
now this seems to be the equivalent cut you just did. but again, variance, and that tree certainly wasnt a heavy leaner.
sink as normal
plunging/boring back cut in middle above bottom of sink but not more than 25mm again, move to leave the hinge, again, at least 10% and leave 10-20% at the back as a 'trigger'
now, this is the major disparity, our technique stipulates removing the trigger wood at 45 degrees, not flat. the reasoning is, it makes for an easier extraction and retreat, and if your saw remains in the cut when you retreat, the tree can't spit it out at you, it also guards further against the wood itself splitting.
as others have said (and i shant go over ppe again) escape routes are paramount, from that video i would have said you had adequate escape routes should you have wanted to take them, but it's hard to say so i cant comment too much,
all i know is an instant fail on my course was stepping behind the tree or into any of the danger zones, and cutting with the saw perfectly flat is the most valued skill. that's the only advice i can give, just always be mindful of what you are doing.
as for only being 22, im only 20, so be careful, take adequate precations, trees can bite hard, and 22 is a short time alive.
be safe
Jimmy