Bus layovers

[Kevin]

Something that always intrigues me, is there a set place for each route to layover?
I ask because Monday morning things kinda came to a head on Priory Queensway, with all the saltley buses parked up at the top, blocking the 66 stop (as is usual), a 67 bendi came up and sat patiently behind the 87 so it could leave, a 72 came round both of them and parked in the 65/67 stop.... 66 then comes and gave up on everything, choosing instead to unload and wait at the 16 stop right at the bottom.
Thing is, this sort of situation ain't exactly uncommon, why can't all the saltley buses unload and head straight round to wait at their own stops?