When creating your delivery areas it is important to know the behaviour of the system when adding certain delivery areas in your distribution method settings and to avoid any UX issues with your customers.
A common issue is where 2 options are given to the customer on the same delivery day. This is caused by adding 2 postcode areas that are similar and on the same delivery round or different delivery round but the same delivery day.
For example if you add the area OX10 and the area OX10 1 to the same delivery round or different delivery day it will display the two options.
How to avoid the duplicate options
When creating your delivery areas ensure not to have any overlapping delivery areas on the same delivery round/delivery day. Pick either a wider area such as OX10 and not including the sectors or add all of the sectors instead such as OX10 1, OX10 2 etc.
This can be used intentionally if you want to give the customer choice over delivery days. This only really works if the delivery areas are attached to delivery rounds on different delivery days.