Standard tone for 面 (mian4 or mian5) when used in words like 后面, 前面, 对面?
Sorry I can't tell the strict grammar rule (about the tone of 面 when used for the meaning of "side, aspect") as a native Chinese. I tried some research, but can't find any uniform and convincing explanation about it. So I tried to summarize it by myself as follows:




light tone only:


  上面, 下面


For 上面 and 下面, without special context, when pronounced with the 4th tone 面 tends to be considered as noodle. 
4th tone only:


  对面


For 对面, 面 can't be pronounced with the light tone, it's just weird.
both light tone and 4th tone:


  前面, 后面, 里面, 外面, 左面, 右面


In these cases 面 is pronounced by light tone more commonly.