Without having some idea what kinds of changes you made when you converted to a responsive design, it's difficult to know why you might have dropped 6 positions.
Did you keep the same urls as in your old desktop site? Did you keep the same content, or did you change the content for responsive? Did you redirect changed urls? How long has it been since the changes were made? Are you taking about desktop or mobile results? Are you taking geo-location into account? Please describe roughly what the situation is (continuing to use examples, as you have).
With regard to the phrase itself, in a large city, eg, it's very possible that
"Blue widgets Cityname" is an extremely competitive search.
It's also not clear whether you're talking about plain vanilla organic results among, say, specific product results that aren't featured in Google's local vertical... but even these can be hyper-localized...
... or, more likely, whether you're talking about more generic results that include "Local Packs" combined with organic, which is really a specialized area of search, for which we have a dedicated
Local Search [webmasterworld.com] forum.
In that forum, I've just posted a thread about the most recent version of a guide that's essential Local Search reading, and you might want to check it out...
2017 Local Search Ranking Factors https://www.webmasterworld.com/local_search/4844636.htm [webmasterworld.com]