jit.desktop - how do I "offset" x,y?

Hi,
Just starting to learn playing with jitter so this is probably a simple thing I'm overlooking..

If I use a "rect i i i i" to set jit.desktop's parameters, I presumed I would be setting top left (x,y), bottom right (x2, y2)

Such that setting x,y to say 100, 100 would define a rectangle from the top-left point 100 pixels from the left of my monitor, and 100 pixels from the top of my monitor.

Then I thought, perhaps the top left corner is 0, 0; but y is negative since it's "down". (eg 100, -100)
This didn't work either....

The bottom right seems to set as expected, but not the top left? What's going on?

Also even regardless of it not producing the 'offset' effect I was expecting, setting parameter 1 (x) doesn't seem to update the rendering sometimes unless I also update parameter 2 (y)