Symptom:

Incrementals are the same size or larger than the Full backup, even if the Incremental was run an hour after the full completed.

Cause:
If this behavior is seen, it is likely that the file set for this backup has the "preserve access time" checked, but "Only check modification times" not checked.
Normally on unix-like systems when we do a differential or incremental, the file will be included for backup if the ctime (change timestamp) or mtime (modification timestamp) is greater than the time of the last backup (so if the file has been modified or changed). Opening the file to read it for backup updates the file's atime (access time). The preserve access times option tells the agent to reset the atime on the file to the value it was before the file was backed up. Setting the atime is a change to the file, so the ctime gets changed. Because of that change, the next backup finds the file has a newer ctime, and so it gets included in the backup again. The Browse and Restore window shows the file's mtime (which contributes to the confusion).

Resolution:

There are two options for making incrementals and differentials work properly with a linux client:
One is to turn off the Preserve Access Times. When a file gets backed up, its atime will be set to the time of the backup. With this option off, the atime will not get reset, to the ctime remains unchanged. Some programs do not like having the atime changed on their files, so turning this option off could have mildly unpleasant consequences if such a program is being used. (I can't think of an example of such a program, and I think that behavior is somewhat rare).

The other choice is to check the option to Only Check Modification Times in addition to having Preserve Access Times enabled. This will ignore changes to the ctime, and only backup the file if the mtime is newer than the last backup. Changing the properties of a file without modifying its contents will only update the ctime of that file. So with this option, changing the owner, group, or permissions of a file (or other file attributes) will change the ctime, but that change will not be noticed and backed up until the next full.

Unless it causes a problem for some software you are using, the first option is the recommended option.