You are right, some strains seem resistant to the feminization process.
Right now, my slurricane is slow to produce any pollen sacs.
I usually just hit a lower branch for pollen, and smoke the rest.
I'm sure if you were to dedicate a whole plant to be femmed, it would do so more quickly as the top buds mature faster.
I also don't spray it on, as I don't want overspray hitting my other plants.
I put the sts in a pump bottle for hand sanitizer so it doesn't actually "spray".
If you add a few drops of a surfactant it seems to help also. I use a product called tween.
Good luck