I'm not for a second saying all crop circles are fake, but a lot of them definitely are, that alone has added greatly to the confusion and mystery.
I do believe there are advanced aliens out there, after all, if there hadn't been the mass extinction event that took care of the dinosaurs, then there would have been reptilian highly evolved species on earth millions of years before mankind came along, another planet that didn't have the same mass extinction could easily have a civilisation millions of years old with infinitely greater resulting technical and scientific development.
I'd love to help with the crop circle field seed bag idea Nev but I live the opposite end of the country to where all the crop circles have been and there are no arable farm lands here, it's all sheep, mountains and lakes.
P.S. the conehead skulls are human, there were cultures that practiced head wrapping of babies to make the skulls grow like that, I forget where it was now. I know sheep with mutations so severe they are unrecognisable as sheep are not uncommon, so I expect it is possible that very alien looking skulls could be those of mutant humans. I think that is much more likely as a scenario that them being alien, largely because I expect alien life would differ so much from humans that they probably wouldn't even have anything we would recognise as a head, let alone a skull.
Human life evolved on earth, science has proven that, the odds of similar lifeforms to us evolving independently is so remote as to be a non-starter, aliens will be totally unlike us, just look at how much variation there is in life on earth, expand your scope to the galaxy and the potential for variation is so large as to be unimaginable.