well that did solve the problem… I imported the original photo into Photoshop and selected the person in the photo using the wand and the eraser to get the desired and appropriate transparency, then imported the .psd into Motion and the Min/Max feature in conjunction with Channel Swap did work as you describe.
on the image with the masks, I removed the masks and applied the min/max filter to see what would happen, and what it appeared to do was enlarge (using maximum) or “crunch” (minimum) the pixels of the image, rather than enlarging image size itself
sorry, I’m very new at this and totally lack the understanding or the vocabulary to explain myself or the problem accurately… but got there in the end.