Handlebar bag sewing and mounting question...

Just a quick question, as I can't seem to figure it out just from looking at pictures online... Do most smaller handlebar bags only mount to the handlebars in two places (the loops that go around the bars)? Or do some have some sort of third attachment that wraps around below the stem (or some other place)?

My mom is very big into sewing and wants to do a project with/for me soon, so I thought a handlebar bag would be cool to carry my phone, wallet and keys and maybe a quick snack. We were just going to play around until we figured something out, but I wanted to make sure just two attachment points was somewhat the norm for a smaller bag like that, and hopefully the bag swinging around won't be too much of an issue.

Additional question: Does anyone have any patterns they recommend? Thanks in advance!