Slower pan and zoom on key or button press

I would like to reduce the speed and step size of pan and zoom in response to clicking control buttons on the vtour skin, or pressing keys. I tried putting the following tag in tour.xml but it does not seem to have any effect. What is the right way?
<control keybfovchange="0.25" fovspeed="1.5" keybspeed="2.0" />


Update: with the following added to tour.xml, it does seem to behave as I would wish:

<control mousefovchange="0.35" keybfovchange="0.25" fovspeed="0.5" keybspeed="1.0" keybaccelerate="0.2" />
So I guess I had just not tried hard enough.