Understanding Finch's "Bird in the Arras

I had a hard time getting a clear image of what is happening in the poem because the language in the poem is difficult so I thought I would write about my process of understanding the poem. I first looked up the definition for Arras and discovered that it is a tapestry typically used to conceal an alcove.  So, something like this: 

Once I had this image in my head it was easier to understand what was happening in the poem. I thought the bird had accidently flown into some curtains and got stuck. Lines 5-9 explain why the bird got stuck in the first place. I believe the tapestry had an image of a Grove with birds flying woven into it which is why the bird mistook it for a place to “passe the scortchings of the sultry Noon”. Line 8, “where imitated Fowl their pinnions ply” was confusing to me at first. I discovered that pinnions is another word for wings and “ply” means to work”. So the tapestry contains images of fake birds flying high which, inspires the actual bird to out fly them in lines 10-11, All the outstrip’s (move faster than) and with a moments pride/ Their understation silent does deride. “Understation” was the only word I could not really define but, I think those lines are essentially saying the bird succeeded in out flying the birds and derides the fake bird because of her success….until she hits the ceiling and then the window. The bird continues to “Flutter in  endless circles of dismay” until someone lets it out through the “casement” (window).