You are talking about emulsion bleeds now. Different function to an air bleed. The emulsion bleed [ s ] above the fuel level is to bleed off some of the signal. That bleeding off could also be done my increasing the size of the MAB. Not sure of the reason for both/either method.
I would say anytime you introduce more air [ more AB ] into the fuel, you emulsify it into a finer mixture of air + fuel; you will then get two benefits: easier to control this mixture via the emulsion bleeds & better combustion of the A/F.
