firstly, just because you're able to eat large portion, don't. Doing so can not only stretch the pouch but it can also cause issues such as slippage etc with the band, every time you eat a large portion you are putting the band under unnecessary strain and continued eating of large portions can cause the band to fail.
If the first bit is sticking, then it's probably too big a mouthful, not being chewed enough or eaten slowly enough, it's down to you to change all of those things.
The only people who can really advise regarding the fill is your provider, but firstly I would try changing how you eat, because there is the argument that if any food is sticking that you have restriction and it is now just down to you to sort how and what you eat to work with the tool you have,