Is there a logic to ב in this context, or is it just one of those "Hebrew is different from English, get used to it" things? I know ב as essentially meaning "in", which is really weird for me in this context. Does it have a secondary meaning or is it just a case of being used differently?
It's one of these cases; but note that the preposition ב has another major meaning other than "in", and that is the meaning of an instrument or means by which the subject does the action - in English it's usually "with". So "She hit him with a bat" - "היא הכתה אותו במחבט". Or "he saw it with his own eyes" - "הוא ראה את זה במו עיניו". (Sadly, in spoken Hebrew this usage os ב lost a lot of ground to עם - people will more likely say "היא הכתה אותו עם מחבט" - but purists consider עם wrong here, and I wouldn't expect it in literature or a newspaper.)
Here "plates" is not an instrument or a means, but maybe it's a bit closer to a means than to a physical or temporal location (the "in" meaning of ב).