Actually, placement of the light bar depends on purpose of use. We who live on this mountain use 40-52" light bars mounted on the cab or on the bumper. Some on the hood, but that is not really an ideal spot. I did mount a 42" on the hood my wife's van which worked out well due to the downward slope of the hood. We use the light bars to light up the world on this dark road due to the large number of elk. My wife has hit 3 elk and 1 deer. My neighbor has hit 4 elk. The elk will stand on the highway and not move at times. I have had them bump the truck while just sitting and waiting for them to move. With the large curved bars we can see way off into the forest. For roof mounts we use a light bar mounting kit from Grainger. Around $100, but top quality.
ps, My friends hit a large bull elk last Sat. The elk was struck by the front end then flew thru the air, its antler going thru the rear side window and then landed on the highway. After they stopped the elk got up and ran off with out a limp.