I figured out where I was wrong! As a test, I downloaded an “external” img file that I was able to run. Its parameters were described:
imgmount d Win95E.img -size 512,63,16,255
Then I tried to create several img files, but none of them worked. In my final desperation, I looked at the downloaded file (Win95E.img), which was written to 131 604 992 bytes in the properties! Where can I see the “virtual parameters” of an img file?
(Sorry if the question is stupid.)