You will never get a "theatrically" acceptable haze out of a fog machine. Typically, a fog machine set on it's lowest pump setting with a fan running full-bore about a foot in front of the fog machine will give you SOMETHING that picks up the beams, but it tends to not be a nice even haze. For added dispersion, point it off stage with the fan blowing on stage. You can fine tune it by checking to see whether you can get a lighter fluid, but not one that is fast dispersing, that may help... I would suggest looking towards hiring in a hazer as required.
You also really want to chill the venue pre-show, then fog/haze the bejeezus out of the venue with the HVAC off and then top up as required. Air movement will kill your effect very quickly due to the high molecular weight of fog fluid.