From how you describe the tear-out and busting through at the bottom it seems like the wood you are working is quite dry but in your overview as I read it, you are using freshly cut trees. Some wood is inherently weak between the rings and prone to separate. It's the case with a stack of sweet chestnut I am working right now and it means paying particular attention down low like that, lightening up on the cuts, extra scoring and like you say altering the angle of the cut, you can try either direction, so if you are hewing but end to top in a forward moving direction, angle your cut forward for example. It's definitely a problem that can be overcome. Around the whorled sections you can make use of the axes' sharpened toe to slice or pare the unruly fibers cutting perpendicular to the axis all the time but moving forward at the cusp of each cut as if you are pushing the cut forward out in front as you move through the difficult sections. I always like to think, if I am hewing along at 60 and come to a knot, I slow it down to 30.