We've had both experiences, so I'd say maybe it depends how wet they are before the poo IYSWIM. Kacie isn't a very heavy wetter either so that could be something that effects it. I've had times where I've thought there was a poo but looked in the wrong side, or down the back when it's all at the front
not smelled anything either and then been shocked a couple of hours later to find a mass of poo
Then I've had other time where it's just started to leak out the side, even though there's not much. Maybe it does depend on the conistancy of the poo somewhat. We're still getting runny
poo though, as we're only doing hit and miss solids for now.
I'd go for use just after a poo for now and see how you fair. We're now using Itti's pretty much full time and I've only had one minor messy leak, IYKWIM.