Undergrad Umbrella fabric and diffraction pattern

[Orthoceras]

It is sometimes said that a distant street lamp seen through a dark coloured umbrella fabric appears like dotted diffraction pattern, as in figure A. However, I have tried several umbrellas but all of them produce a blurred cross, as in figure B. The umbrella fabric superficially looks like a regular 2D grating, with warp and weft threads crossing at right angles, as in figure C.
I guess modern umbrella fabric is somehow different from old umbrellas cloth. What might be the difference? Does anyone happen have an umbrella that produces the dotted diffraction pattern?

The image of a dotted diffraction pattern at the left is from an image at wikimedia commons

 

[Keith_McClary]

I had an umbrella that produced a pattern. The five I have access to now do not. I have some fabric with about the same thread count (that was a coat liner) that does produce a pattern. I speculate that there could be a waterproof coating on the newer umbrellas.

 

[Orthoceras]

Waterproof fabric was invented by Charles Macintosh in 1823, I doubt that any 20th century umbrellas would have had no coating.

Another explanation might be the composition of the thread. I put the umbrella fabric under a microscope. It turns out each thread of the umbrella fabric is composed of more than 10 filaments. This type of fabric is called a taffeta, apparently. In the photo, possibly more light passes through the B-areas than through A-areas. Then the diffraction pattern is dominated by the filaments. The filaments are not spaced very regularly. As a result, The diffraction pattern due to B dominates, and it is much wider and more blurred than the diffraction due to A.