What kind of defects or struggles are you observing? One thing I noticed over time is that in the beginning my sour dough was not active enough. I started feeding it the day before preparing the sourdough for baking, meaning I added one spoon of flour and one spoon of water and left it at room temperature for about 3 hours.
The sourdough preparation for this recipe takes about 8 hours at 27 degrees C, I do that in the oven with just the lamp on. At the end the volume is about doubled with a lot of visible bubbling activity.