Increasing the number of IR emitters won't help, as they would all emit (roughly) the same distance of beam.
Depending on the scatter of the IR emitter, you could increase the number but I doubt it would be worth it. The dome in the top acts as a kind of lens to disperse the beam anyway - remember that it is a laser (but at a IR wavelength of ~940nm) and lasers have a narrow scatter; that is to say that the beam itself does not radiate from all over the emitter like a lightbulb does. It may well have a viewing angle, and you could possibly work out the size over coverage at certain distances, as if it was a spotlight, but I'd be tempted to just build the damn thing and test it!
All LEDs emit light from the top (domed) part, with the connections (legs) at the bottom.
Just stick it all in one of these boxes. Drill a hole in the side and push the IR led out and glue in place.
http://www.maplin.co.uk/Module.aspx?...sures&doy=23m6