Sophos Central Update Caches - what happens when you manually assign devices?

Question

Anybody know these answers 
 Many thanks 
 Hi we have two Sophos Central Update Caches on our network. 
 At the minute 2000 devices are associated with Server 1 and 2 devices associated with Server 2. Both Servers are at the same location/site. 
 No devices have been manually assigned. 
 How does Sophos decide which Server the client connects to if they are both same location and site? 
 Is there a way without manually assigning devices to balance the devices across both servers? 
 If we manually assign some devices - If the server they are manually assigned to goes down do they then try to update from the next (or remaining in our case) Server Update Cache in our network to update or straight to Sophos severs to update?

RBGE · Accepted Answer

Whoops, my mistake - apologies for the incorrect information then. That's what I get for not double checking my information before posting! 
 For info to anyone else finding this post at a later date, the full KB on manual update caches is located at community.sophos.com/.../122577

StephenMcKay · Answer

A small edit to RBGEs post: 
 If server 1 goes down and clients are manually assigned to it, they'll attempt updating from Sophos instead. As far as I know, there's no way of load balancing this without manual assignment. 
 The clients would try server 2 before attempting to update from Sophos; all Update Cache servers are evaluated before falling back to Sophos for updates. So manual assignment would be an option for load balancing. 
 
 Stephen