oh your UI button is on the 0x0 parallax? I think I understand.
Maybe try using scrollx and scrolly?
Create UIbutton on Layer "HUD" (0x0 parallax)
Create SWAT on Layer "Human" at
x: (scrollx - (viewportwidth / 2)) + UIbutton.x
y: (scrolly - (viewportheight / 2)) + UIbutton.y
There's probably an easier way, but I think this should work.