Quote - Does your client require the figure to be in the pic? Or so prominent?
Does the pic need to be realistic?

No, the artwork is for a book cover and there is no need of realism, but there is the need to give the idea of an hollow world, and bisides realism is diffucult task.
The difficult is to avoid to have a "poster like" background, giving the idea of a depth of field in this unusual landscape.

Quote - I was just thinking of many old Sci-Fi covers from 50's-70's.  Many had pictures that were not true to reality.

Agree! :)
Thanks for the suggestions! :)