I don't use HPW, I use a glider kids staple but I have the same issue.
They eat most of their fruits and veggies but don't lick their bowl clean for their mixture. I drizzle honey on it or mix a tiny bit of fruit juice to add fruity flavoring.
Nothing I have tried works all of the time...it's very random. I think they(mine any ways) go in eating spurts and sometimes eat more and sometimes a lot less.
I will be making them new staple this weekend and am going to try OHPW and see it they like it any better.