In the process recipe you are using you need to set the output location root folder to "image folder".
I think this way of Graham's is the better way to do. If you use Bart's way, you have to reset the output folder each time you move to a new folder of RAW files.
I confess that it took me a long time to work all this out and set C1 up the way I wanted to. So let me clarify Graham's suggestion, at least as I understand it and as I have implemented it, because I found C1's options in this area confusing. This is for sessions on Windows.
In the "Output" tool tab there is a tool called "Process Recipe". It has a series of sub-tabs: "Basic", "File", "Adjustments", etc. Choose "File". Then in the "Root Folder" option you select the "Image Folder" option. That does what you want.
Further, if you want the processed TIFF/JPG in a sub-folder under the RAW folder, then specify that folder name in the "Sub Folder" option, e.g. "Processed", or "Output" or whatever.
If you want to systematically append something to the output file name for that recipe, specify it in the "Sub Name" field and then use the "Sub Name" option in the "Output Naming" Tool.
The reason I found all this confusing is that there is an "Output Location" tool in that tool tab, but as far as I can see, you can't use it for this approach. There isn't the option to choose "Image Folder" in the destination option, you can only specify a fixed output folder, which might be what some people want, but isn't a flexible and general approach. I honestly think that the output options are a bit of a mess in an otherwise excellent product. Once you understand them they work, but it was far from clear and took me a long time to stumble across the "File" sub-tab.