I have found that choosing a stare point about 5 meters in advance of the front edge of the mat works best for me. When helping to instruct beginners, I often make a chalk mark that far out at approximately the correct angle for their bowls’ bias. This way the beginner gets a clearer idea of whether (s)he is properly controlling their delivery angle.
The rest of us must struggle to identify slight imperfections in the grass or carpet to stare at. I have found recently that squatting on the mat while looking down at the far bank helps me choose a stare point that is truly on the aim line. There is a bonus. After I stand up and assume my erect delivery stance, all this time holding that stare point, I deliver my bowl more quickly, because the longer I have to focus on my stare point the more likely my view of it will slip! As a consequence, I bowl better and faster.