I'm convinced that on what I spend, the fraction is way more than 1/3; I think it might be north of 2/3. The clicks on and off the page are just way too quick and consistently so for it to be a human. That said, I'm not sure that's what's happening here.
Yes- mobile is a disaster. I can't imagine anybody profitably advertising on mobile. I've asked this group before and basically nobody has ever deliberately clicked a mobile ad (one guy said he did once, iirc). I have a hunch that the people making money off of these ads know this, too. It might be good for branding, but in that case you should only consider CPM-- CPC is your enemy here.
As I gear up for an advertising campaign, I'm looking pretty closely at channels.
Maybe https is just breaking some fraud bots?