My suggestion would be that;
Cool down:Rather than a on/off skill make the skill like "speed fiends" skill of raptors.Use only and leave it skill which has a cool down for a second use(even that can be left out when it is untoggleable).That provides two things
-Still gives the ability the eldar to outrun in certain circumstances
-Because it can not be toggled.The eldar has to wait or deal with the FOF accuracy reduce through the process.
And if anybody thinks that FOF isnt overpowered in the hands of a good player I want my WA Guardsmen back .(Also with ripped of content )