Follical size will more accurately help you figure out if she is close to ovulating. You can check by letting the snake move through your hands. I usually try and position my thumbs together along the belly and gentle squeeze. It's easier when the follicles are large because it's almost like counting golf balls in a sock. I'm not sure if that's any help, and hopefully someone more articulate can describe the process.
In either case I just keep putting the pair together until the female refuses him.
Cause when push comes to shove you taste what you're made of
You might bend, till you break cause its all you can take
On your knees you look up decide you've had enough
You get mad you get strong wipe your hands shake it off
Then you Stand