The answer to your original post is here (apparently, 90's are not allowed) if you are looking for a UPC reference.
706.3 Horizontal drainage lines connecting with other horizontal drainage lines shall enter through forty-five (45) degree (0.79 rad) wye branches, combination wye and one-eighth [1/8] bend branches, or other approved fittings of equivalent sweep.
As for the slopes in the pictures posted, these are just general references as to the "best" installation. In the codes, you will find a requirement for the minimum slope of a drain line, but there is no maximum (it can slope to vertical).
I didn't read the entire thread, so I don't know if this was already answered.
Thanks for coming back to this. My manuals contradict your comments so please stand by while I find these "manual" comments and post for you. This is not to challenge your intelligence but to help be get to the bottom of what I think I understand. Thanks again for your help.