Hey Ugh!
Thanks for the kind words! Really glad you like it.
I think I see what you mean.
Some skin creators deliberately scale the thumbnails to a size that suits them. Others leave it up to Comicster.
Take a look at the "Maximum Thumbnail Size" in the options dialog (Tools|Options -> Thumbnails tab). If the skin's leaving it up to Comicster to determine how big the thumbnails should be, then that's where it's set.
The only thing you'll probably need to do if you change that setting is regenerate the thumbnails. Click on the folder, or title, or issue that you want to regenerate thumbnails for, and then click "Tools|Reload Thumbnails". That'll re-create them with the new size.
Hope this helps!
Matt