What can I do to keep my cats from throwing up heir flea pills?

I give my cats the confortis flea pill monthly. They are both having frequent problems with keeping it down for the full hour that is required for the medicine to work. To my understanding of the medicine is thrown up within an hour of it being given, then you need to redose; if it stays down at least an hour, then the medicine should work. One question I have is what if the cats throw it up really close to the hour mark like say at 50 minutes or 1 hour, 10 minutes? Does it work or not? I can't get a clear answer from my vet or the packaging. They both just say one hour. And that's when both my cats tend to throw it up - either just slightly under an hot or just slightly over an hour. And they both still have some fleas but not as many. So I don't know if the medicine is working or if it's just kind of working. We've tried several topicals in the past that haven't worked. Is the medicine likely working or not? And if it does need to stay down longer how can I keep them from throwing up? I've tried giving it to them after they've ate enough (dry food) to line the stomach like the packaging says. I've also tried giving it to them after a bigger meal (dry food). Either way they throw up. What can I do?

I have a cat who also throws this up. What helped us is to give it in two doses about 8 hours apart so there isn't as much of the medicine to digest at once. That has helped tremendously. Sucks because it doubles the amount of times I have to shove a pill down her throat but its been a lot less wasteful!