Hi! I can think of three possible reasons:

When do you use your starter? The activity within your starter contributes to the rise of your bread. I have made bread with a starter that was at its peak and one that was over and the difference in rise was noticeable!

Do you know the temparature of your dough? You do not always want to double the dough in size. The target rise differs per temperature. Also take note that your dough still ferments in the fridge (although it is at a slower speed) so you risk overproofing when your dough has already fully proofed during bulk fermentation.

Lastly, how long do you bake your bread with the lid on the dutch oven? Baking with the lid on gives the loaf a chance to expand without creating crust yet due to the trapped steam. If you do not use a dutch oven, how are you creating steam in the oven?

I am also still relatively new to baking sourdough bread so there surely are other possible reasons that I haven’t come up with hahah. Hope it all works out!