I'm not sure I would use that approach because you will be tiling below the camera as well as above so you are building a bunch of pixels the camera would never see. Offsetting the tile center as the camera moves won't buy you anything. Motion Tile Output Height works as a percentage so if the camera started at the default Y position of half the comp height you could calculate the percentage based on movement like this:
c = thisComp.height/2;
cpy = c - thisComp.layer("Camera 1").transform.position;
r = cpy/thisLayer.height * 100;
value + r * 2
Here's how that works. You take half the comp height and subtract the camera position so if the camera was at the default Y position you get zero. Then you calculate the ratio or percentage by dividing the cpy (camera position y) by the layer's height and multiplying that by 100. The last step is to take the current value of the Output Height and add the ratio (r) to that value. Since the Output Height expands in both directions from the Tile Center you have to multiply that value by 2.
I did this in my head and I think it will work.
Personally I'd just motion tile the layer and adjust the position so the bottom was at the bottom of the frame when the camera started moving and the top was at the top when it stopped. I wouldn't worry about animating the motion tile.
Thanks for the response! I actually ended up switching over to AE's CC star burst and just changing the height, I'm not sure what was going on before but it's working perfectly now.