Correct, in the current iteration of the rules, defeating a 1 CD enemy and gathering Tinder from them would give you 1d6 Tinder, while defeating a Formidable 3 CD enemy would give you 3d6 Tinder. The GM is of course free to adjust values if they feel like something has significant value or ambient energy (harvesting from a small pile of coins vs. from the throne room of a forgotten king).