The reason that the model decision comes after physical design is because the model should be built to support your instructional choices (which includes classroom design)—not the other way around. What this does is ensure that you adhere to students and teachers first and foremost, instead of adhering to what a model may or may not require at the outset. The design steps are intentionally ordered such that choosing the model is the last thing you do. After considering student needs, teacher needs, space constraints and desires, technology needs, etc, there will hopefully be an instructional model or combination of models that align best to all of your design considerations. Of course during the Refine and Iterate phase, the design of the classroom should be tested and improved to better serve your students, so as in all things innovation nothing should be set in stone!