Oven spring

Often my sourdough loaves exhibit fabulous oven spring, but they spring a little too much sideways instead of springing high. I get a very nice ear and the whole top opens up nicely. But it still spreads. I know that my starter is very strong and active so that is not an issue. Is it gluten development? My hydration level is at 74 to 75 percent most times. The crumb is nice and open and consistent throughout. But I see some of these breads that people make that grow so nice and high with strong sides, and still open up beautifully across the top. However, mine open up beautifully across the top as well, just not as tall.  Is it a fermentation problem, or a structure problem that I may be dealing with? I use a professional quality stand mixer and the dough appears to be very strong when I do the window pane test. It almost feels like rubber, it is so strong.  Is it possible to develop the gluten too much so that the bread is facing resistance and lacks extensibility? I am new to using my mixer for kneading. I would like to continue because I have hand issues and hand kneading is taking a toll on me. I am using the large kitchenaid commercial mixer, so it is very efficient at kneading dough. Perhaps I should shorten my mixing times, or is it something else I am missing? I do one stretch and fold, and from that point on I do coil folds until I see about a 40 to 50% rise to the dough. That is when I shape it and place it into the bannetons. I refrigerate over night. I do a proofing test with my finger in the morning. If it springs back too fast, I will proof it some more, but most of the time that is not necessary.  I use a cast iron Challenger covered bread pan and I put a couple ice cubes inside it to create even more steam. Does anyone have any suggestions as to what I can do to make my sides stronger and my bread spring higher?