The A”H’s heter is based off that since there is no hirhur therefore there is no problem of erva. The whole sugyia there in brachos is based off this assumption. There is a difference in “proper” erva which is forbidden even without concern of hirhur and between the additions that chazal added that are also forbidden because they generally lead to hirhur even if at that moment there is no hirhur.
But I don’t think you properly answer the OP’s question