if I need to add some more pasta, I just put any type of pasta I have in a bowl of boiling water and then microwave it. small amounts like that will cook in a short time that way. I usually cook it 3 mins stir and cook it another 3 mins then drain it and stir it into the H&S.
In addition to what Phil says, try and find some really small pasta pieces. I’ve got some called soup pasta, intended for minestrones, but it’s smaller than macaroni and is probably good to try out. Spoiler, I haven’t tried cooking it with Mac & Cheeze!
If I have a lot of powder left at the bottom of the bag, I dump it on top of the next bag I’m opening, and try to keep a good eye on the balance of pasta and powder as I go along, but it’s especially hard with the Mac&Cheeze. In fact, this time, because I find the Cajun Pasta a lottle too spicy, I added the last 100g of Mac & Cheeze to that.