Here is a summary chart for the images I measured central and arc angles on.  There is clearly a lot of variation. The bottom line is that the collagen-like portion is flexible, and likely relates to the ability of even mutant (missing small parts of the collagen-like domain) to still function, but with the collagen-like domain is totally missing…. the function changes considerably.  This was research by ……a long list of scientists other than myself.

Here you can see for yourself that there is an acute angle and an obtuse angle in almost every view. That there is also an arc to the collagen portion of the molecule. So while the diagrammers got part of it right (see this post for a summary of the SP-D diagrams)…. straight arms for SP-D molecules are “fake news”.