I reduced the supplementing when my babies (two girls at different times) were still pretty little (2 weeks old) and were only drinking a total of about 12-15 oz a day, so my experience is different. I was probably supplementing about 4-5 oz and I just stopped and started nursing more and my supply caught up to their needs.
In your case, I think stopping one or maybe even two feedings would be fine. And just increase the number of times you are nursing if possible. Take a day or two and just nurse whenever the baby wants and see if you can decrease the supplementation necessary.
My scale was a lifesaver for me. I weighed before and after feeding so I had some idea of how much they were getting. I could also track their weight gain (or loss). It gave me great peace of mind, but also made me somewhat obsessive. Just remember that it is normal for weight to fluctuate some day to day (when they poop, pee or eat).
And I will definitely say that cutting out the supplementation was a total leap of faith on my part that my body would catch up. I wasn't there at the time, so I just had to trust it. And both times it worked and we ebf from that point on until the girls were 18 and 20 months.
Good luck to you.
Jennifer