yes, that's what I was doing wrong, mark. the default v4.1 loads with a lo-res lashtrans file.  when I replace it with one of the hi-res files, the lashes render o.k., no matter how bad the light/shadow/render settings. so the very dark, distinct lash shadows were the result of the lo-res file (see attached render).

but looking at peoples' eyes up close, and looking at stock photos, I'm not seeing any lash
shadows, hence I daresay it must be rather difficult to take a photo of an actual human and
get distinct lash shadows,  although the laws of optics dictate that it must be possible.