Don,
Accually I dind snging harmony easier then the melody in most church music. The Melody covers a large range, but often the harmony is a much simpler part. Personally I find singing the alto part down and octave works best for me, the tenor part is too high (I can get it, but not without warming up my voice) and the bass part is way too low.

If your the only one singing harmony it doesn't matter what you sing, if it doesn't clash too often that is the way you ment it. If others are singing harmony though, then you better be right or you will clash too often. The melody is of course much easier, but with practice you can do it.