It depends on the cu. in of your box but it will be tight. You may be able to if your box has a minumum 27 cu.in. This allows a 12/4 and a 12/3 with a device grounds and a clamp-- not sure what you are using. Personally I would avoid it and put a jb above, if possible
The PIA factor does not into play in deciding where and when to splice, it comes from dealing with instructions someone who is not there and has no idea what you are dealing with trying to tell you what to do.