Do attic vents or rafter baffles need to be as wide as the rafter bay?
A vented soffit allows air to flow in.  The ridge vent allow the air to flow out.  The purpose of this attic venting system is to keep the roof deck at approximately the same temperature as the outside air across its surface so that melting snow won't form ice dams.  The venting system is not there to cool the attic volume itself.

If the baffles are not properly installed so that they guide the incoming air up to the underside of the roof deck, air may be blowing through the insulation, a process called "wind-washing".  This will displace loose fill insulation like cellulose and will reduce the R value of batt insulation which relies on still air for its effectiveness.