It was the intention that the dropdown should be set to File if the "From File" preset was used, but it seems it never worked properly. I have updated the script to 4.1 where I removed the dropdown altogether so the presets work like intended.
For your second suggestion I made an update to the 4.1 version so that the filename can now take an absolute path. So in your case, put the file wherever you want then put in the full pathname of the file as shown below. If you save this as a preset it will always use that file.
