I should have thought of this earlier, but I was focusing on the topic of diluent instead of looking at the problem you were trying to solve!
Liam is running low at night, so you want to lower basal. But an alternative might be - rather than lowering basal, trying an extended release carb at night.
These bars are designed for slow release carbs that last a very long time.
Minimize Spikes and Avoid Blood Sugar Swings
Our Bars metabolize slowly and convert to glucose for up to 9 hours, helping you maintain stable blood sugar without dramatic highs and lows.
It might be worth a try.
I have used bars like this before when I was doing MDI and had too much basal. Since you can’t remove the basal with MDI, this was an easy fix.