"One thing that has to be mentioned that it doesn't matter if it is a fixed head or mechanical there will be certain times when you absolutely pipe your shot through the vitals and you don't get much blood."
"It's not always the broadhead it's just the animal that has been shot."
The only possible reason that you would not get much blood from a perfectly hit animal is-A DULL BROADHEAD.(or maybe a mechanical head that failed to open).
-Sharps