A carefully planned and placed base course is very important for a patio or a continuous walkway so that individual pavers will not heave or settle over time during winter freeze and thaws or when underlying soil becomes saturated with water and turns into a muddy fluid.
Your project is not a continuous patio or walkway, though. Each paver will be well separated from its neighbors and there's a change of elevation at each one too. The generous spacing will make it difficult to even notice if one paver shifts, rotates, or tilts a little bit relative to another. In fact, I question whether loose pavers sitting on gravel and sand may actually be more prone to movement than they would be when sitting directly on and surrounded by soil. Think of the lateral forces involved if a person jogs or pushes/pulls a wheelbarrow or other cart along the path.
My personal opinion is that a base course of gravel and sand is unnecessary for this project. I'd compact and screed the soil so that there's a firm, flat surface (whether level or inclined) and lay the paver right onto it.