Right now Tom Wolfe is doing testing on exactly what you ask about. There's definitely a few options as far as twin tips or twin cap adapters (if you are not familiar with the adapters, they essentially let you hook up two tips on one nozzle body).
Tom [and PAMI] are doing testing on the best application for dual-tip spraying, seeing what is the most effective way to spray while maintaining the best coverage. Anticipated to do two [maybe 3] years of testing, in crop and in lab testing. So far they've done one set of in-lab testing, and were pretty surprised by the results in a way. On a whole, switching to a dual-tip does definitely increase coverage, but they found similar results seemed to be achieved when even spraying with one [coarser] nozzle at an angle forwards and going fast.
Again, depends on what fungicide you are spraying (i.e. Head blight vs. Soybean rust, etc.) as it make some difference how you want your penetration/coverage. For example, for headblight, Tom found so far that using a single tip at an angle (can't remember what he preferred for an angle - some reason I want to say 30°ish) and going fast causes the spray at hit its terminal velocity pretty darn close to the target (Headblight), and since the droplets are big and you are going fast, the spray starts travelling a lot more horizontally. With the horizontally moving spray, it will hit the majority of the chem on the front of the head, but something like 30-33% of the chem ended up on the back of the head due to a vortex as the spray went around a head.
BUT, the whole idea means you'd have to rotate your boom ever time you were wanting to spray fungicide, which isn't reasonable for a lot of guys. I think the difference between well-picked dual tip spray and one spray going horizontal is one of the "5% more benefit", which isn't a small gain, but it probably isn't worth the time for some guys. If you have a Wilger setup, there is the dual-tip adapter that you could use with a single tip and cap off the back side of the adapter if you wanted to try it out without buying a whole set of tips.