Phrase_prefix boosts prefix above phrase?

HI all,

I'm doing a city search and I'm experiencing a strange (or not) behavior.

I'm searching with phrase_prefix and it looks like it is giving more weight to any document with the prefix than any other that has an exact match.


searching london, I have Londonderry coming with more wight. even New London comes first.
Same happens with miami vs Miamisburg
or Lima vs Limassol and Limay..

Why a prefix-ed word has more weight than a complete match one?

I've tried to use type phrase only, but this causes that the search "Chicag" won't bring chicago.

any ideas?

thanks in advance.