earplugs falling out of my ears

Did a swim this morning and decided to try the Mack's Aquaplugs INSTEAD of the Mack's Pillowsoft silicone plugs that I normally use.   About 1/2 way into my swim, I could feel the Aquaplugs falling out.  I had my swimcap pulled tightly over my ears at the start of my swim, but inevitably it creeps up and that's when I felt the earplugs coming out.  It was really frustrating, as I had to stop and readjust them.  I'm pretty sure I inserted them correctly...doing the "twisting" motion to set them in properly.  Anyone else have this problem with the Aquaplugs?  Perhaps they just don't fit my ears correctly.  I think I'll stick with the squishy silicone ones.