first of all
i know that you have two routers, three switches and a web server
i'm not sure of some terminalogy that you mentioned in your post such as 6m ,12m
before i say anything i'm not an expert nor a professional and i do not possess any cisco certifications or any industrial certifications.
but before i go on i have noticed that your design based on the 3 layer design or similar
but i noticed there is a slight mistake with the design or as i think.
i think you need to connect the switch which connected to the server to both upper layer switch not just the middle one, in case of a fauiler.