I find the quality of the hull is the bigger factor in a good crimp (technique and press of course matter too)
Yep. And, I've found speed to be very critical with less-than-top-shelf hulls (at least with hand tools and/or the Lee Load-All).
The low end Federal hulls I loaded a few months back, for example, had to go straight from the crimp starter to the final crimp, as fast as I could move them. Otherwise, the crimp did not set; and I had to open them back up and start over. You need to get some heat in that low-grade plastic, or it doesn't play nicely.