OSE and B/X: Combat movement through enemy spaces. What's your house rule?

As best I can tell from the OSE tomes, there is no explicit rule about moving through enemy spaces in combat. It says "Melee attacks are possible when opponents are 5' or less from each other". So, based on that, RAW seems to imply that opponents who aren't currently in melee, and maybe not able to attack, are unable to prevent each other from moving 'through their space'. So what do you do at your table for this?