ActionScript 3.0 ::movieclip In Edit Mode - Objects Won't Centre ?

I'm trying to get my new character system working with my fairly simple physics system. I have code at the bottom of the page which demonstrates my collision function. The most important line, which I've bolded, is:

Code:
currentPlayer.y = hitBlock.y - ((hitBlock.height * 0.5) + (avatar.height * 0.5)) ;

I wrote this myself, all logic dictates that it should work. We start with the position of the centre of the block. We add half of it's height, to reach the top surface of the block. And then we add half the avatar's height, which should give the exact point to put him at so that his feet touch the top of the block. This code should be able to account for any arbitrary heights of block or avatar. But it's not working, my avatar is stuck just a little bit inside the block.As far as I'm aware, my math is perfect. So the only source of the problem I can think of is in the objects themselves. I'm not fully sure what the registration point is - logic would dictate that it's the recognised root point of the object, and when I tell an object to go to a coordinate, I would guess it's moved so that point rests exactly on the coords.I'm not entirely sure how to change it though.When I look at my movieclip in edit mode, it look like this.

The image has been downscaled so it's tricky to see the details, but I want to draw attention to the fact that there's three points of interest on it. Around the middle of the bounding box is a white circle,I think that's the registration point. A bit above that, on the figure's upper torso, is a crosshair. And to the topleft of the bounding box, just outside of it, is a second crosshair.What's also interesting is that when I deselect the movieclip, the white circle and the second crosshair (outside the BB) vanish. But the one on his chest stays put.If I move the movieclip, all three of the above things go with it. I can select the circle and drag it around, but not the crosshairs.my collision code:

Code:
//if main hits a block, then stop jumping
//this loop will check a hit test with any block
for(var i:int = 0;i < world.blockHolder.numChildren; i++)[code]............