I'm HQ10 with roughly 25K medals.
I don't keep record of medal scores but from what I remember on attack from -37 to +20 (for a 2 star).
On defense from -19 to +42.
AFAIK the medals are only defined by your level (may be HQ level or base score). And the medal difference to the opponent. So If he's got more medals than you, then you get a multiplier>1 for wins. If he's got less medals on you then you get a multiplier>1 for losses.
However there's a glitch when the medal difference between you and the opponent gets bigger as 50K, then that mulitplier reverts to 1. (don't know if this was fixed on the last update)
(Rebels/Android/iOS). Just PM me here/LINE:lleyleber or request in game with a meaningful text. If you want to take part in wars, lv7+ is useful.