Now I'm wondering about other senses. I can readily imagine sounds and pictures, but it took my brain some time before it figured out how to imagine smells and tactile sensations when I asked it, like a muscle that is rarely exercised.

Since my imagination layers on top of my existing senses, I wonder if aphantasia is really about the (in)ability to induce sensory hallucinations at will (and to what extent). That's about the only way I can make sense of it personally, given my own subjective experience.