Can the size of the Temp file be increased? If so how and where is it?

I do a full backup on Fri for a file that is 175 gig in size. The first several weeks the file would be compressed to 108g, which is want I want.
The last several weeks the file is being broken into 4 different files. Why would this happen?

Run a full backup of folder X on Friday. Mon - Thursday a differential of this folder is done. This seems to be working fine. The problem is : Can I name each days backup by the days name(Mon, Tues, etc.) instead of the insane Backup4all naming procedure? If I could it would solve my problem which i...

Thank you. Just wanted to make sure.

When a differential save is performed does the system look for any change to any file in a folder and if it sees any change it then copies the entire folder vs. just the changes file? Is it possible to save only the specific file that has changed?