Cover during mobi conversion

[Aonghas]

Hi - I'm new to Calibre and have fairly general question - every time you covert from epub to mobi, Calibre creates a cover and the relevant TOC entry, and will use the first page if there is no cover present. Is there any way to prevent it doing this?

Have searched the preferences, but the only option you're offered is on the conversion dialogue box, and then only to change the cover image, with no option not to have one at all.

Have found some posts in the past that relate to this, but haven't yet found a workable solution.

Cheers