Is my waist size too small for these shirts?

Hello, I'm planning to buy some Charles Tyrwhitt casual shirts (like ) and according to their for small casual shirts:

To fit collar: 14.5-15"
To fit chest: up to 37"
To fit sleeve: 31-33"
Actual chest: 42.9"
Actual waist: 41.3"

According to my measurements, my neck is 14.5", my chest is 36" and my 32" sleeve dress shirt fits me fine. However, my waist is 31-32" and I'm not sure how much wide the waist on my shirts should be. I'm not sure whether I'll wear these tucked or untucked yet. Will that change things? Also, if these ARE too big, would a tailor be able to fix that? Thanks for the help.