When dealing with very large trees in comparison to the bar length I have done a very open face cut then a plunge cut into the center of the notch and swept from the inside of the tree out, then you connect to the inside sweeping cut from the outside(this leaves a slot in the hinge and can get you in trouble on a weak tree). You can use a fairly small bar to cut a relatively large tree. I have found it easier to meet(or at least get close) to matching the cuts than starting on one side of the tree and working all the way around the tree for the back cut, and you will also be able to achieve a hinge closer to 80% rather than somewhere in the middle.
I also like a thin(top to bottom)tip on the bar I use for doing plunge cuts as it doesn't hardly chatter. Make sure you don't take your rakers down to far if you plan on doing plunge cuts as that will also make it chatter, all the more on hardwood to.
I need to go over to my buddies to help move his chicken coop to a different location(it's right where I plan to drop a couple of the trees).
I will get some pictures of the before. This is one of the larger ones out of three I already took care of, my hinge was a little off as well, but the power lines were still in the air when I was finished lol. Directly behind the stump is another one of the larger ones that I will be cutting, you can see it is missing a lot of bark already, perfect for this winters wood. To me this is the perfect sized tree to work with for firewood.
I think I may have already posted these, but couldn't find them.