FileWidgets read from kdeglobals the property "MaximumSize" under "PreviewSettings" to decide if a preview will be generated for that file.
There is no current GUI to change that file size limit. On the other hand Dolphin ignores it.
This patch aims to fix that by adding new configuration options to Dolphin.
As I am a noob it currently has a flaw. It is that it doesn't pick up all the configuration changes 'on the fly' but only after restarting Dolphin.
If the check "Local files" is checked then the file size limit affects immediately. But changes to the checkbox itself only take effect after restarting dolphing. I know why it happens but I couldn't code a solution. Maybe Nate can give me a hand or point to someone that can.