You got some great advice especially getting rear ballast and carrying very low at all times. For cutting into huge tall plies like you have, picture how you would slice a piece of bread or cheese off, only in reverse. That is, from the bottom up.
What works for me well is to drive into the pile low with the bucket dumped slightly. I try to bury only the tooth bar and then curl the bucket while raising it up at the same time. Like "slicing off" a 2" to 6" wall of dirt. this will depend on how strong your loader is of course. You must always work within the capacity of it. You can also drive into it slightly as you are doing this, if the pile allows it.
Once you get a good slice going, sometimes the top part will crumble down, sometimes not. If it doesn't, that's where I would reach up to pull some of the higher stuff down....but always with an empty bucket. Personally, I try not to exceed the top of my hood or not too much past eye level while I'm cutting off slices this way for safety and load reasons.
So in reality, the way I do it is not so much like you would pick up a small pile of dirt, driving into it and through it, then curl to pick up. It is more like slicing bread up-wards.