When you are doing warmups, try to get out of your usual rehearsal standing arrangement. I’m particularly interested in using a “zipped circle” to focus on vowel and timbre matching.
Have the choir form a circle, and then, like a zipper, come together into two rows facing each other. Now, do your normal warmups – maybe one focusing on lip vowels. Move one position counterclockwise on each half-step modulation until you’ve done a complete cycle. This gives each singer the opportunity to hear each other singer’s sense of vowel, timbre, etc. It has potential for tuning ears to the voices in the choir, coming to understand the variation in vowels and timbre that are present in the ensemble, and more.
Brief side-note: today is the 1,500th consecutive day I’ve written a post for my website. Streaks matter and are a powerful motivator. For me, anyway.