4k film workflow

hello, fortunatelly I still have clients that shot film, and then do 4k scanning and color correction in order to have a 2k or 4k dcp.
I have some questions regarding size and framing. first, i´ve generated optimized media starting from the 4096*3112 dpx sequence, and changing the clip atributes to Cinemascope to have the normal aspect.
I´m running some tests and everything works fine, but I have the following question.
Is there any setting to correct the difference between the full aperture scanning and the scope academy size (the scan includes the sound area of the negative) I´m correcting this with a zoom and pan value in the ouput sizing, but I prefer a standard setting.
The other question is, when I try to export the 4k files, if I leave the original time line setting to full aperture 4096*3112 I get the right picture but with the black strips top and bottom, that means a lot of extra size in the files. But if I select the 4096*1716 DCI option, instead of rendering the central part of the picture and have the same image without the black strips, Resolve is changing the size of the picture.
I only want to render the part of the picture I´m using....in 4k sequences that means a lot of processing and storage...
Any suggestions? I´m sure Im not the only one dealing with these files...
Thanks in advance
Roberto

Set project to desired size and play with resizing options in project settings.