If you are absolutely sure of getting a place at Westfield - and you would be happy to be offered it - it would make sense to name it as one of your preferences, rather than 4 schools which depend on how many / few DC have higher scores than yours.
If you have to be given a 'non-ranked allocation', this will be the nearest school for which your child qualifies and which has a place to offer. Note, this is not necessarily the same as 'nearest school'.
The year this happened to DD, we were very lucky that the school she would normally have been allocated in the circumstances was actually oversubscribed for once...
Thanks for the information regarding the non-ranked allocation. Not sure I would be happy with Westfield, but I think that's the only "nearest school" listed when I check with hertsdirect website.