WOW, I am impressed that you can do all of that!!  I would love to see what you are working with as well.  That often can give an idea to those of us who don't work with something THAT TRICKY.

I would only have a single suggestion that might work.  I do use this myself with good success, however, I am not embroidering on a spider's web as you are. . .

I use basting for many of my projects.  However, I don't just baste the outside of the area, I often baste, depending on the situation using an "X" through the area.  After all, basting can be easily removed and any basting under the embroidery is just - well under the embroidery.  I often baste smaller, not larger than the project as well.  Once again, it can be 'interesting' to remove the baste, but one has to do what one has to do.  Further more, basting does not always mean via the machine.  You will know where your trouble spots are, place the stitches as you need them.

Hope this helps!

Pat, The Avid Embroiderer

Pattiann always has great advise and I agree with what she said as well.  Then, I thought of two more things that may help your project.  It is often not just a single thing that will make it perfect, sometimes you need a pinch of this and a dash of that!!

If you don't have suitable fabric to do that testing on, go to Goodwill and other shops to find something close to your fabric.  For a few dollars, that go to a great cause, you can be testing even more close to your project.

The next, on that testing, use pull compensation (pc).  I have been embroidering for 14 years and only recently found how to exactly use that feature.  All the explainations were very confusing for me.

This is waffleweave and has similar issues to seersucker.  I neglected to put a topping on this example, but it does show that pc is needed.  PC just gives a more wide satin or zig-zag stitch over the underlay.  You can see that the satin stitch, which I stopped before the underlay, is too narrow to cover the underlay.  I did not properly prepare this 'discovery sew' (my term for finding out how your project will look) because I was checking the software rather than the whole project.

I don't use any adhesive on this fabric, I use Floriani's Heat-Away.  It has an 'etched grid' on the side to place against the fabric and holds it very well.  I would not use an adhesive (and after reading your query, I did try it).  The adhesive holds the fabric, even if it is out of alignment.  On waffleweave, that would show but not on seersucker.

Test is the key, the right fabric and knowledge makes it work.  Keep GOOD notes!  If you don't have Evernotes.com you need it to keep those little bits of info that won't remain uppermost in your mind.  In Evernote, I have "notebooks" for the different fabrics, another for software ideas, another one for project problems and solutions and another notebook for my personal stuff, including my medical information.  Evernote 'syncs' between your pc and your phone so putting info on your pc will be in your phone when you are out and about.  There is a free version and I LOVE MINE!  (I don't get paid to say anything!)

Pat, The Avid Embroiderer