That is what I read as well. For the shorter OCI the P1 or M1 filter does a better job. I saw testing on a site by a member and his data backed it up. Even if I were to run an oil for 15,000 miles I'd rather use a Pure 1 filter and change it out at 7,500 miles than run the Amsoil filter the full 15,000 miles. Wish I could find the results.
Please post the data. I would love to see it. Thanks.