First thing with bonuses that, while they are a nice perk, they are never guaranteed. So even if you negotiate for a $1m bonus, they are not obligated to pay the full amount, or any amount, at year end.
That being said, do you know anyone at that company, or at least anyone in a similar type position in that field? I also don't think it would be unreasonable to reach out to your contact at that company and ask what their bonus system is like.