Switched my starter from a wet sponge to a stiff levain and my loaves went from flat to domed in 3 weeks
I was feeding my starter at 100% hydration for almost a year and my boules kept spreading out flat in the banneton no matter what I did with shaping. A baker at the Saturday market in Ferndale told me to drop it to 60% hydration and feed it twice a day, and by week 3 the dough was holding a tight windowpane and my last 4 bakes all got real oven spring. Anyone else run a stiff starter for country loaves or do you keep yours wet?
Kept mine at 100% for years and never had a flat loaf problem, so I'd bet the fix was the twice a day feeding and not the hydration. You changed two things at once, which means you don't actually know which one did it. Drop it back to wet but keep feeding twice a day and see what happens.