Okay, first, about the whole "scroll to see" thing, I agree with you in the sense that if you're caught up on a series, you may not end up scrolling down.
But if you're so aware of this problem as a reader and want to support the artist, why don't you just rectify this situation by scrolling down anyways???
Encourage your readers to keep their adblock off for Tapastic (other websites, whatever, this is about Tapastic) and also add in a little nudge for them to scroll to the ads just so the impression is made. They don't have to click on them, just have to have them on their monitors so it registers as an impression. You're turning something into a problem that you, as a reader, clearly know the quick and easy solution to, and can easily just let your readers know that if they want to support you through ads, all they have to do is scroll down, even if they are updated on the series. I guarantee you most readers are fine with doing this, especially considering most of them maybe do want to support you through other means, but don't have the money. Readers then know that they're supporting you by just looking at the ads, and they don't have to be interrupted during the reading experience. Just raise awareness and let them know that it's there.
Second:
As far as I know, you are not actually required to offer milestone goals. If there's a default goal, then set it as $1 and say that they'll get access to supporter-locked content, which could be anything from day-early pages to doodles that you do in your spare time. You don't need to offer the personal livestreams or the commissions, you don't need to offer merchandise and prints, and you don't need to offer anything higher than access to supporter-locked content if you don't want to.
Yes, having those goals is a bit of extra incentive for someone to want to support, but Tapastic really tries to aim the focus of the Support program to the artist, and makes it pretty clear that what you're supporting isn't really the comic itself (or comics), but the creator delivering the comics. This is why you can't throw money at one individual comic (unless said comic is on Premium, which not many series are).
The extra goals and gimmicks are your choice. Access to supporter-locked content is the bare minimum required. I've seen lots of creators who don't offer a whole lot of rewards but still pull in supporters, and that's because they deliver content that people want to put their money into. That's really all you have to do. It doesn't matter how many rewards you have listed, if you as a creator aren't delivering content people are confident enough in to support with real actual money, then the whole point of the Support program is lost.
As many people have pointed out already, the Ad Revenue program wasn't built to pull in millions of dollars a day - it was built to give creators a tiny share of the money Tapastic pulls in every day through their own traffic, traffic that you need to earn yourself. It's amazing as it is that Tapastic is a free-to-use platform (vs. places like SmackJeeves that won't give you the full advantages of their platform unless you pay so much a month) and still tries so hard to put some money in the pockets of the creators that make up this place and got this place to where it is today, with all sorts of methods like Ad Revenue, Supporter Program, and Premium. There aren't a lot of other places that do that, and still manage to look as good as Tapastic does without annoying the shit out of us with pop-up ads and mysterious audio blurbs that we can't seem to find where they're coming from.
Alls I'm saying is, I think the biggest problem you're facing here is the fact that you're not retired and swimming in cash yet 
Which is gonna take a long time and if you're expecting that right away, you're in the wrong business lol (this isn't meant as a swing at you, it's just extra food for though, especially for other creators who may have gone into it thinking this very same thing).
Make your readers aware that the ads are there. Do a comic on them, or make a public post to your subscribers. Ask them if they can turn off their ad-block here and make sure to scroll past the ads so they can help out the creators they love so much. You'd be surprised what people do for content they enjoy reading, even if it's only pennies a day. But you need to make them aware that it's there and how it helps you as a creator deliver the content they love so much. Do your part, and they'll do theirs.
