Making a .dream file, trying to center my animation using a hybrid file

I'm trying to do a few things with my .nwa animation using a hybrid file, having some trouble.

First off, my animation is 840px X 525px. Deskscapes is stretching the image to fill the desktop background. I just want to make my animation centered in the middle. I set the HybridWidth and HybridHeight, which stops Deskscapes from stretching my animation. But I don't know how to center the animation in the middle of the desktop.

From what I've gleaned from the HybridDreamFormat.pdf, I need to specify the XAlignment and YAlignment in the hybrid file. But here's where it gets confusing:

; X coordinate alignment mode  
; 0 = from left, 1 = from right, 2 = from middle, 3 = % from left, 4 = % from right, 5 = % from middle
; % are defined as value / 1000 
XAlignment =

I think what I need to do is set the XAlignment as 25% from the left boundary to make my animation centered. But the .pdf says '3 = % from left', uh...

How should that be typed? "XAlignment = 25%"  doesn't work.

"XAlignment =  25 / 1000 from right" still doesn't work. "XAlignment = 25% from left" doesn't do anything.

It just defaults to 'XAlignment = 0'.

My animation is also stuttering and slowing down while be played, not sure how to deal with that issue. Do video files have better performance than .nwa animations?

Appreciate any advice.