Always make sure you have a comfortable setup when you want to copy something in your environment. Suppose I want to copy a self-portrait in the mirror with the paper flat on the table, I have to move my head too much between the paper and my subject. I also get distortion in the drawing more quickly (image).
With a workstation A3 or A2 (see internet) you can quickly solve that problem (image). Without a workstation you can clamp your paper to a hard underlay. This way you you are completely flexible, also outdoors.
If you are using a painter’s easel, always make sure that you are not looking over your drawing arm at the subject. If you are right-handed, your subject should be slightly to your left. Outdoors, you may have a sketchbook with you, but even with a hard surface for your paper, you are flexible.
Exercise: try out what feels good in terms of posture and setup when drawing a subject in front of you, indoors or outdoors.