user35553 is right, setting the
FingerLow values via
synclient should produce the effect you're after.
synclient is a convenient way to play around with the various options the Synaptics driver offers, but if you’re happy with your changes, you’ll probably want to make them permanent for all users rather than running
synclient manually or at login.
Normally you'd do that via the xorg.conf file, but Ubuntu, along with several other distros, has effectively deprecated the use of
xorg.conf in favour of device-specific scripts inside
/usr/share/X11/xorg.conf.d. You may or may not have this directory, and if you do, you may or may not already have a file inside it called
50-synaptics.conf. Create the directory if necessary, then open the file (substituting gedit for your editor of choice):
sudo mkdir /usr/share/X11/xorg.conf.d
sudo gedit /usr/share/X11/xorg.conf.d/50-synaptics.conf
Edit the file to include Option lines that set your desired FingerHigh and FingerLow values. Mine looks like this:
Identifier "touchpad catchall"
Option "FingerLow" "10"
Option "FingerHigh" "16"
Save the file, and when you restart, your new settings will apply everywhere in X.