My measurements are from newly-dead animals, from the top of the shoulder down to the bottom of the chest behind the leg. This is not taken at an angle, but "between the pegs," as ingwe put it. In other words, I am not tilting the tape from the highest point of the shoulder backward to behind the leg, but making a measurement at 90 degrees to the main line of the body.
This is the most consistent measurement we see when using the reticle as a rangefinder (the point of this post), partly because we can almost always get a look at that depth, even if the animal is quartering away. Also, some animals have more hair at the front of the chest, or even skin. That's why I measure them the way I do.
That's also one reason I don't get chest measurements off mounted animals: Shoulder mounts do not usually include the back of the shoulder. Also I have measured the same animal both in the field and after it was mounted, and the two measurements do not always agree. In every instance the mount has been larger than it was in real life (or real death). I suspect this is because taxidermists, like most humans, tend to stretch things.
