A long time ago, I had two editors tell me they greatly preferred synopses that were written the same way the jacket copy on a published novel is written. I’ve seldom had this fail me.
But and however. There is one HUGE difference you have to take into account. When you’re actually writing a query/synopsis like a flyleaf, you must include the ending of the novel. The reading public doesn’t want a flyleaf to give away the ending, but an agent or editor must know the ending in order to properly judge the novel.