When using a touch capable screen selecting the read icon in a chapter list can be difficult due to the small size of the button. I use a microsoft surface for reading on, and sometimes it will take two or three taps to accurately select the read icon.
I see you didn't mention any problems taping chapter titles. But read icon size is exactly same as chapter title. That only means there's no problems with icon size but something else.
I don't notice chapter titles as much. Like it was said before, the chapter titles are longer, so it might be easier to select them. The more likely thing is that I only select a chapter title once, when I'm about to read something, so if I misclick once it's less of a big deal. The read icon I notice more, because I'm more likely to select it multiple times when I've forgotten to mark something as reading before I begin, and have to go through and select all the chapters I read.
Going down the list and having to click them so many times is what made me realise that.