Testing/Samj/Frame At06B 2017 Frame painting

I’m using often the frame in object.
May I get an indication on how is calculated the frame dimension?
Because I noticed some discrepancy with respect to what I thought, to have something clear to say I used it on a 3000x1000 image, setting the size value to 10% and vignette to 0.
I got a frame with a width dimension of 250 and a height of 188.
May I know the calculation applied?
Thanks to Sylvie (and to any other person knowing and replying)

I try to attach the result

Used max contrast to let the frame be more evident.

Using it (same parameters) on an image 1000x1000, the frame results of 84x84.
So I understood that the frame size is applied on the image size reduced by percent of frame entered (1000-84-84 = 832; frame 84 is 10% of this adjusted size). But what about width drastically different from height as in the original post.

@samj Ping. This is one of your filter and the OP has a question.