All my online visual research can be found on https://uk.pinterest.com/shahjmiah/pins/ and this contains the links to the original source for these images.
I can see that the a giant 3 legged robotic monster is normally the focus for HG Wells The War of the Worlds book covers. The Invisible Man cover always has the main centre point on the Invisible man himself, direct and to the point. The Time Machine book covers have a mechanical feel to them including circular shapes. Also the word HG Wells is very prominent sometimes even the font size being bigger than the title and I believe this is because the author is the draw for many readers. I will use these to help me with my designs.