How definitive is tail suck?

Newbie breeder here, hopefully having at least one clutch this year. :salute:

I'm wondering how certain you can be that a female is gravid, if you witness a tail suck?

My understanding is that they build, then ovulate, and ovulation is when the tail suck occurs. I've witnessed what I think is tail suck in a couple of my girls, but they don't look HUGE. Everyone says that when they ovulate, you'll know - and based on the many pictures I've seen of ovys, they just don't look big enough.

Unfortunately I only learned today that the underside of the tail also looks very "sucked in" during ovulation, so I didn't look for that.

I'll post some pictures momentarily so you can see what I mean.

http://images.tapatalk-cdn.com/15/08...b150b7cc50.jpghttp://images.tapatalk-cdn.com/15/08...0ed03689db.jpg

These are my two girls (different snakes, same morph [emoji14]). The second picture is the much more obvious tail suck.