Is This A Place To Use The Stirrup Attachment On My Cobra?

[rmr]

making this case, and would like to use my cobra machine to sew on end panels. there is about a 3/4 "overhang edge- see picture- not sure what you call it- I don't think its a gusset. with the standard plate on my cobra machine I cannot make the curve in the 2 corners to sew. Is this where I should use the stirrup attachment??

If so- there were several threads I saw a while back( can't find them - so sorry for asking again) that had multiple different recommendations about tighten tension on the needle thread tension, others I thought said you had to do something with the bobbin thread tension- so what is it. If I attache the stirupp plate and sew on some scrap leather, the bottom side of the stitches look loose??

I have attached some photos