There are ideas to provide Goblins some kind of bonus for/in flank or rear attacks. How could those rules look like? Is that something people want at all?
They're braver when flanking an enemy, but the enemy isn't more bothered about being flanked by them than by other units.
Flanking doesn't make them suddenly stronger or more powerful in some way though, they just get braver when they think they've got the enemy at a disadvantage.