I have a yellow indicator also on a new filter that was installed in a 500HP C12 application. It always, if reset, runs up to the same yellow point in scale and has not changed since being installed. This indicator measures the vacuum being pulled and not the exact filter contribution. The change from where this indicator starts out will be the added change due to the filter restriction changing. Our "zero" or start point sits in the yellow and not in the green. It tells us that the vacuum is higher and more restrictive than you would like but the filter may not be the main culprit.
Peterson is a good outfit but a technician telling you to get a less restrictive filter can only come with some loss in actual filtration (pore size) unless the filter has vastly more surface area than others which is always limited by space. You may want to understand that if they have a filter that is less restrictive, what it is you are giving up. I would trade off in favor of some restriction over poor filtration causing engine component wear.
The air intake system includes all of the components involved, each having their own restrictions, including the filter being one of the components. I have often looked at the size of the coach air intake on the side and thought that it looked awfully small. Not sure if that is part of our problem. They (Monaco, Beaver) could have kept using that same part as displacement, turbo boost, and engine sizes increased.
I have purchased a Donaldson Extended life "Endurance Filter" and when I get to install it, will have a result if anything changes using that filter. By design it is a better filter with more surface area and better particle entrapment characteristics. Not sure if it will help with the air intake restriction issue.
Here is a link to the Donaldson Endurance filter. The technology they use is a very fine media web above the filter surface that traps and holds the particles away from the main filter media. That reduces filter pressure drop over time as contaminants mount up. There is a graph showing that characteristic. This filter type will not solve a restrictive air delivery system that is inherent in its design but would reduce the added loss from the filter component over time. I consider it to be one of the best filters on the market.
http://www.donaldson.com/en/engine/support/datalibrary/000165.pdfLater Ed