I'm waiting for my back to feel better ...
But, I did experiment with adding various ingredients to the filler to make it less viscous (not working) and using vacuum bagging in order to put equal and higher pressure on the latex.
The later has merit but I'm fighting with 'vacuum pump mist' (google it) as I don't want to breath vaporized oil.
Since the filler I'm using is too stiff I've ordered some more 3M 31180 Finish Glaze. The batch I had went bad after sitting too long. The idea is to build up the general repair area with filler, but to later impregnate the pattern using a very high quality glaze. The pattern need not be very deep and glaze can be very thin. It's a bit runny, which is a good quality for this repair. It's also a 2 part, so it hardens quickly.
Just in case you want to experiment with vacuum bagging, the idea is simple.
Adhere a plastic film around your repair area with duct tape or similar sticky tape and apply vacuum.
To get a vacuum source into the film I stole a screw-on schrader valve from one of the race car wheels. I then added two large washers and two large rubber washers to the mix. Cut a hole in the film and sandwich the film between the rubber washers and tighten the whole affair.
See
https://www.veneersupplies.com/products/Bag-Stem-Assembly.htmlAlthough I have a real A/C pump (garage sale) a compressor from a fridge works too. HF also sells them. Various fittings and an old R-12 A/C gauge set round out the tools.
Apply your filler to the repair, tape the latex in place, cover the area with your vacuum film and tape and then apply vacuum.
Do note that in this pic that the vacuum valve is too close to the repair.
Also, I may need a mat to place over the latex in order for the vacuum to be distributed over the enter area. Look up 'composite vacuum bagging' to learn more.
I'm not saying this is the final answer, just some thoughts on how to progress towards one solution and get those smart minds out there working.