Honestly, I think small two blade broadheads are the culprit for poor blood trails in many cases. I've been shooting single bevel two blades for a couple years now and really like them, in most cases I get more of a hole then a slit like the typical to blade but in every case that I have gotten the typical to bleed slit which seems to happen when I hit ribs on the exit I always have gotten very poor blood trails.
In contrast, I shot three blade Wenzel's, snuffers, or four blade Muzzy phantom for about five years and never had a poor blood trail. I didn't get penetration on the shoulder though that's for sure.
I've shot two deer this year which were hit perfectly through the lungs, One of them went 20 yards stopped and stood in one place for about 20 seconds and then keeled over. I got some blood splattered at the shot which was a pass-through and then absolutely nothing on the trail including the place where the deer stood.
The second deer went about 80 to 100 yards with an absolutely perfect shot, I found one drop of blood and about to the 50 yard mark. Again this was a pass-through.
Both of these shots were double long shots but I have had the same experience with two blades on heart shots. I've also had pretty good blood with many two blades and particularly with the single bevel heads..
One thing about heart shots: It depends on where you hit the animal in the heart, remember the heart is a pump, if you hit the ventricle or pressurized side of the pump then lots of blood on the way out to the body. In contrast, if you only hit the intake (Atrium) side of the pump you'll end up with a low pressure pump, kind of the same is trying to suck water out of a straw with an air exposed hole in it?