It's so frustrating when the tools Amazon give us aren't up to the job. The AMS dash doesn't report income accurately, and the only way to find out if someone is borrowing my books is to repeatedly load the book list on the author page for each supported store, to see whether the rankings are climbing.
(A borrow doesn't show up anyware except as a jump in sales rank. It's only visible as pagereads when people finish the book they're reading now, and maybe 2 or 3 after that, before they finally start on mine.)
As an experiment, I've been running ads at a higher total daily budget than I want to. It seems to be the only way to gather the data I need (CPC/CTR/effective targets)
Some days I see a big spend on ads, with just enough sales to justify the spend, and a KENP which is about the normal average, if a touch higher.
It's only when I look closer at the breakdown that I see something pretty significant: Today, despite a modest overall page read count, a large percentage of those reads are for 'first in series' books. In other words, the ones I'm advertising. A couple of them are 2-3 times higher than the page reads for book 2 in the same series, which means something is bringing in those new readers - and it has to be the ads.
The sales ranks for those books don't support these figures, which could mean these folk borrowed the books days ago, when I first boosted my ad spend, and are just getting to them now.
Anyway, if I'm reading the data correctly, the readthrough could eventually turn the ads into decent earners. If not, I'm throwing money down the well.
Usual case, with advertising.