It is not always a good idea to put the tree trunk protector as low as possible, for two reasons.
First, you often create an unwanted downforce on the nose, which increases rolling resistance and causes energy-sapping drag of rope the through the rollers. In most recoveries it helps to have a force pulling upwards, or at least not with a downwards component.
Second, the force required to recover the vehicle if it's not a direct line pull increases. Take a look at the diagram - the actual force required to move the casualty in the desired direction is represented by the line C. If the pull is at an angle, like A, then the line gets correspondingly longer, so more force required.
So you might well exert more force on the tree by putting the protector lower than higher!
Of course, the reason you generally go low is because that is where the tree is strongest - the greatest width and least leverage. That is true, but the point here is to think about where you place your protector, and that may, or may not be close to the tree trunk base. This is particularly true if you are using snatch blocks in a way which either multiply or reduce the load on the anchor point relative to the casualty.
