To encourage muffins to rise higher, we start baking them at a higher temperature (425℉/220℃). Then, reduce the temperature to 350℉/177℃ to finish baking. This "start high, then go low" technique for muffins is one we shared in our cookbook, Evergreen Kitchen: Weeknight Vegetarian Dinners for Everyone. And, it's also backed up by other baking authorities like TheKitchn.