Click through rate vs number of users?

Is it normal for banner ads to have lower click through rate as the number of users increase? I’m not talking about changing the refresh rate. I mean increasing the number of impressions by having more users download the app.

I seem to recall hearing about this phenomenon in these forums…

Yes, that is definately true for all types of ads, including notifications. Users get used to the ads, and no longer click on them. That’s why you always need a steady flux of new users to keep your incoming stable.