I never actually got better at that. I developed a coping strategy that actually worked out best for everyone, which was simply to sing loud enough to not hear the sopranos. It wasn't blatant to the audience I don't think (I hope...), but it meant I could focus on my part and our conductor had a little bit less of a discrepancy in the sopranos overshadowing us. It can't have been too bad as I only continued being encouraged as we got a few more altos the following year.
I have a version of The Sound of Silence on my phone, an MP3 that has followed me from a desktop computer in another country. And it has the two parts separated by channel: tenor in the left ear, bass in the right. For years now, I've been studying the bass part of this song, intermittently, whenever it comes on. I always sing along with that one, hum that one, listen to that one.
I think I've almost got it :)