This is just a theory, but ive heard several rumours of this.
In HD apparently you strafe further, but fall with less force, which will make you bounce slightly lower, i am pretty sure of this as FOR EXAMPLE, on crash if you try and do the bounce in standard, but fail, you WILL die, on HD, you will NOT die MEANING you fall slower.
BUT in Standard, you fall with alot more force, hence bouncing higher.
Just a rumour/theory..
Repp and Thank if you wish..