Agreed. The "dome" section of the rubber probably aids the rubber in opening and closing of the valve.
Guessing that the thinner mesh area is where the rubber is allowed to flex.
I'm not an expert on the material, but it looks like the mesh material is the same throughout the old one. The manufactured one certainly has the mesh. I'd like to say all went well with the rebuild, but I still have an issue to look at next week. Once under pressure it worked fine for several cycles, then decided to stay open. I'm looking at the valve (Richdel 205) that they are using to port off the water as a possible cause. May be that it doesn't want to close under the low flow from the exhaust tube. I'm going to verify that it will close at the valve by capping the exhaust flow, then proceed from there. I knew this was bad news from the beginning, but I'm determined to finish even if it means cutting it out and installing an electric valve.