Hey Plankton, nice snaghunting!
As to fibre pulling-don´t be afraid of boring some of the heartwood, leaving two hingestraps on sides. A well-grown hardwoods of such dimensions usualy have enought tensile and even yield strenght in pressure to be able to hold most of the tree´s weight just on 3/4" wide hingestrap. Without a shade of crushing the wood. And about 1/4" (or even narrower in some species) strap across the dia. of a 30" hardwood can frequently easily withstands ALL the weight of the tree in pull along the grain. (The strenght of the wood of hardwoods in pull along the grain is almost always 1,5-2,5 times the strenght in pressure along the grain, depending on tree species, soil condition, part of the year... Mainly on them.)
So when the tree goes over, the front part of the hingewood don´t crush under the pressure as it does in softwood, so as the tree goes over more, the tension applied on the back of the hinge rises rapidly and concentrates mainly in thin portion of wood just on the back of the hingestrap. And because the wood withstands soo much in pull, it breaks not almost "all in one" as in "typical" softwoods, but breaks gradualy in thin layers-which leads to consecutive fibre pulling just before the grain breaks.
So means to weaken the hinge to a level where the hinge´s crossection yield and tensile strenght are somehow less than possible pressure and pull loads from the mass of the tree are welcome. It´s not a GOL or sissiness, it´s just a little of applied basics of Material science.
Maybe the first paragraph is too "scientific" for immediate orientation in what´s to be said, so for simplification:
In most hardwoods, the usual hinge, as can be easily chased all-day long, is too massive and capable of withstanding much higher forces, than those applicable by the tree´s own falling mass. Hence the fibrepulling comes from and making the hinge smaller (by boring the heart) prevents it.