4.) If you're finding the shoes to be too tight across the top of the foot then it is likely that the overall space in the shoe, what we call the shoe's volume, may be low. This can be due to just having a thicker foot, a high in-step, or even a thick sock.
5.) Some shoes within a single brand may have different volumes despite having the same lasts. This is common due to the use of different materials in the upper part of the shoe, some being thicker than others. For example, a waterproof shoe may have less volume than its non-waterproof counterpart because it has a waterproof membrane.