That's an interesting question that I asked myself when we first started looking at that issue, and it's a common comment that I've heard.
Under the OBPS, as I prefer to call it to avoid mumbling the words, the large emitters will have a baseline, so those that are more efficient than the average will have credits. Those that are less efficient and emit more will have to pay or buy the credits from those that are more efficient.
Smaller emitters that are not required to operate under the output-based system will be able to participate if they want, and in the event that they are more efficient, they'll be able to sell their credits to large emitters that are not as efficient.