I have never had Handoff experience on my iPhone 7 on iOS 10 and my MBP 2016. The day I got my iPhone 7 I just flashed iOS 11 beta 1 on it, so don't have any idea, but I think you might be talking about a bug that I think is a bug. Do correct me if I am wrong.
Let's say we are in Messages on MBP, and I am typing "Hello" to a contact. Now, for me, the expected behavior would be that if I use Handoff and open Messages on my iPhone, it should have the new message screen, that contact, and the text "Hello" typed already.
This behaviour is not replicated vice versa as well. If I am on iPhone and I type something, I expect that I can open the handoff messages icon and it will have the text pre-filled.
Again, is this not how Handoff and Continuity work? Is this a bug or am I understanding it wrong?