The best article I've seen which explains this is by Ratcliffe & Rogers from the US Navy. "Balanced FUEL Injector Effects on Inflight Engine Vibration".
This article really says that balanced injectors are a bit of a band-aid to cover some really bad inlet manifold design. The bit I don't understand is why no-one has had a go at making tuned inlet runners. The Lycoming TSIO540 in the current Stationair is a pretty nice setup and seems to embody many elements of best practice. The inlets on our TSIO 360 are a disaster and are probably only saved by being force fed air.
Apart from the regulatory hoops, it would be easy to make something like that. I would expect that even just doubling the diameter of the longitudinal pipe which acts as a plenum chamber would help. I don't know why no-one has ever tried it.