"You stand to the purple curtain, and not to the brown one."
Translation:A lila függönyhöz állsz, nem pedig a barnához.
It is not easy to translate these sentences into English, for precisely this reason. See the discussion here
Ultimately I think it's better to not think of this as literal motion, but more of a figurative. The suffix is describing the relationship between Te and függöny; for example, the curtain is not the direct object, so it is definitely not függönyt.
And probably there is some purpose for standing there - it is not that you are randomly standing somewhere and by coincidence there is a curtain near you - so even though we are OK with near/next to in English, függöny mellett, it's not the best in Hungarian.
No, the purpose or objective of standing is to be to the curtain, even though it makes no sense in English, this reason has to be expressed, and is done so in the suffix of függönyhöz.