i have never had 7 create the system reserved partition. plus 8.1 should be searching the entire drive for the boot info from 7 to add it to 8.1's boot loader.
"If you have ever installed Windows by yourself, you may have run into the situation where Windows setup tells you itís going to create a System Reserved partition for system files. The size of this partition is 100 MB. The exact prompt is
"To ensure that all Windows features work correctly, Windows might create additional partitions for system files."
You only get this dialog and this additional system reserved partition in certain scenarios. Normally, if you click OK at the prompt, your partitions will look like this: