It takes a bit of practice, but you can get the hang of it (my highest score was a little higher than 1700). It didn’t maximize for me, which made it a bit hard to gauge sometimes.
Maybe throw some alpha/translucency on the knives to see the needed slices underneath? I get why they’re so close together, as you can line up the slices, but they also feel in the way a bit.
I also find it interesting what games decide to ‘punish’ and what just gets a pass. So I let it play out and there’s an end where it stops, making it a score attack, so it sort of makes sense to not break a heart over a not completely sliced object. But then you can ask, why have hearts at all?