The minimum focus distance for the canon 100mm macro lens is 31cm. If we took a picture of the eyelashes at that distance with a Fullframe camera, the "in focus" depth is 0.31 cm using f8(DOF calulator).
For a 1.6x camera, we want to get the same field of view (same magnification). So to do this we need to back up the camera and take a picture at 50 cm away from the eyelashes. So this picture will have a "in focus" depth of 0.61 cm. That 0.61cm doubles the "in focus" depth of a FF camera. That is a huge advantage for most macro photography.
Also the len's minimum focus length is the same whether you use a crop or FF camera. So a crop camera will get you a greater magnification of the object with the 100mm macro lens.
However pixel sharpness maybe better on a FF camera by a pixel peep amount. This is because the amount of digital information is usually more compressed in a crop camera. That is a whole different issue. Same with noise level, and gradation of tone. All will make a difference if one likes to pixel peep.
Now that I re-read your post, you can easily determine if your 100mm macro can take the eyelashes picture. Google Field of View calculator. On a FF camera, you will have a 20.72 degree field of view. So at 40cm focus distance --- width of picture = 2tan(10.36) x 40cm. So the width of picture is 14.625 cm or .57 inches. This means you can really get close and take a photo of the eyelashes. .57 inches of the eye is on your entire camera frame. The photo looks like it also has a 1/4 to 1/2 "in-focus" depth (0.6 cm to 1.2cm)
So according to the DOF calculator at f16, your "in-focus" depth is 1.15 cm. Looks like you can do it. However, I leave it to you to verify my calculations. I suppose to be working at work right now.
