You would have to be allergic to get a reaction They small fangs, are reluctant to bite anyway and mates who have been bitten have not had much of a reaction. However, an Eastern Brown that size would require hospitalisation if it envenomed you. So it's not about the size.
No, size doesn't mean anything. I've been bitten by a marshy. Within minutes my thumb felt so tight I could have stuck a pin in it to release swelling, next morning my whole hand was fat and sore, and right up to my elbow. It remained very sensitive to cold and no strength in my hand for a week, then it was like it all disappeared overnight. It was my fault he bit me. I was trying to peel retained shed off him and lost grip of his head. He reached round and latched onto my hand near my thumb.
Another guy on here says he has been bitten and almost died from a Marsh snake bite.
Its never safe to assume you'll be perfectly fine with a mildly venomous snake bite, regardless of what it is. Everyone reacts differently to the venom and its components. It'd suck if you were tagged, didn't think anything of it and then you happened to be one of the few people to have a potentially fatal reaction.