Parse the first and second character in the path?

That's a novel solution! You can logically set the path to lower case without modifying the actual path that in the request sent to the pool. This allows you to remove some switch cases. You can also combine multiple cases where the action is the same:

 
 when HTTP_REQUEST { 
     Parse the first then second character in the path 
    switch -glob [string tolower [HTTP::path]] { 
       "/a[a-l]*" { 
          pool reward-uat5.123.com_AA2AL 
       } 
       "/a[m-z]*" - 
       "/b[a-l]*" { 
          pool reward-uat5.123.com_AM2BL 
       } 
       "/b[m-z]*" - 
       "/c[a-d]*" { 
          pool reward-uat5.123.com_BM2CD 
       } 
       default { 
           Requested URI was a leading forward slash only 
          pool reward-uat5.123.com_AA2AL 
       } 
    } 
 }  
 

Aaron