No expert. But it says here:
"If a noble metal like stainless steel has a large surface area in contact with the electrolyte while the sacrificial metal (such as aluminium) has a very small surface area in contact with the electrolyte, then the stainless steel will generate a large corrosion current which will be concentrated on a small area of sacrificial metal."
https://www.assda.asn.au/technical-i...etal-corrosion