I have used the method you describe & yes you need to smooth out secure each section with the clips before pinning. I don't understand why you are using the spray basting with this method. Pinning is enough to secure the sandwich for quilting.
However, I do prefer the floor method. Lay backing - taping it to the floor, lay batting, then top. Smooth each layer out before adding the next & then start pinning from the center out. I have the least waste of batting using this method as it is easy to line up 2 sides & then cut off extra on 3rd & 4th sides by putting my cutting mat between backing & batting, line up & trim using ruler & rotary cutter.