Walking, but every time I used sweet scent before first trying a synch it ALWAYS advanced the frame and jumped me into a battle 3 ahead. It might have to do with the fact that every one of those times my poke wasn't in the grass as well.
However, if this bike / walking is my problem, can you help me out by telling me how many frames are advanced when you ride a bike and sweet scent? Like, if I was on frame 15, and I called Elm for that frame, and then used sweet scent, what frame would I battle given that the next 7 frames are all the syncher's nature?