Exciting news - intarsia pulling sideways DOES cancel out felting pulling up-down! The image aspect ratio remained nearly the same:

I learned something about felting intarsia - if the image is less than two stitches wide, it doesn’t show at all. All those delicate one-stitch lines I’d intended to indicate, say, the fold of a petal just made the finished object very indistinct. And in general I think the image should be much larger to catch better detail. So I’m going to need to produce a much larger set of drawings (and perhaps a larger purse!)

Another thing I learned - hubby’s beard clippers work GREAT for shaving felted swatches. Natch.