Domes are most effective at the center of a cross-shaped church, over the nave, rather than over the altar (which would be at the head of the cross).

Then you can stick a huge icon of Christ, Pantocrator up there. Beautiful, I tell ye.

Jam

Large, deep domes even over the nave create acoustical problems, sucking up sound, as it were. The era in which those structures were built was an era where intelligibility from the alter through the nave was not a priority; the ritual needs are different now, and the designs from the earlier era when intelligibility was a higher value (for example, the Roman basilicas of late Antiquity and their imitators) are better models. I would reserve domes for baptisteries and chapels and narthexes. (Also, modern HVAC needs will, except in perennially temperate climes, make such domes problematic in sheer cost of climate control over time. The more traditional basilican model adapts much more readily to modern needs, interestingly. When you hear an unamplified schola sing in the old Roman basilicas, you can get a sense of the authentic context for the sung Roman liturgy; it's very different from the nimbus of sounds one hears in vast Baroque and Gothic piles.)

I've never heard acoustical problems in Eastern churches with domes. My church in my hometown has a nice, smallish dome, and short arms if you will like you said, and the choir stands in one arm and I've never had problems hearing them, even when they sing pianissimo.

For a very interesting acoustical church, see the parish I was chrismated in. They have a geodesic dome for the whole church, with a cupola at the top and a wonderful Pantocrator icon in. The acoustics of this church are so good that the priests can't hear confessions near the iconostasis, which is where they are traditionally heard, but had to build actual confessionals off to the sides, because a whisper in the front of the nave could be heard clearly in the back.

Perhaps before when I was speaking of nave-domes, I meant cupolas?

@Jam: Confessional booths are a Latinist encroachment! Was "geodesic dome" in 19th century Russia? Of course not! And alas, Onion Dome web site has retired and no longer publishes new funny news. Is outrage! --Fr. Vasiliy

Does this mean polyphonic antiphons sung with 4 choirs in St Mark's Basilica in Venice have poor audibility?

Actually, I should correct myself, the exterior domes are on drums, but the interiors are not - they are relatively shallow compared to domes of later eras. If they were, the sound effect would be worse along the nave.