How the grid is placed
Panels divide the safe area, not the trim, so the outer borders sit exactly on the safe line and nothing important is near a cut. Column gutters default to 0.1875 in and row gutters to 0.25 in, the usual print proportions (the eye crosses a row before it drops). Rows can have different panel counts: 2-3-2 puts three narrower panels in the middle tier, 1-2-2 a splash over four. Typing 3 x 3 gives three rows of three, and 2 x 3 three rows of two, the way the presets are named. The table lists each panel's size and position from the top-left of the canvas in inches and pixels, so you can also draw the grid by hand.