converting comic mobi for KPW with customized margin

I installed JBPatch on my kindle paperwhite and used that patch make
the margin of reader smaller.
So the page setup -> output profile "Amazon Kindle Paperwhite"
is not the most suitable one for me.
When I convert a .cbz file to .mobi , the images do not make full use of the screen.
Then I set comic input -> Override image size, it dose not work and even make the
images not as clear as before.
Please help me! :help: