If etching the surface creates more gas production, it's probably the surface area. Thanks very much for the help, I think I understand these devices much better now, and may build some electrolysis device of my own.
I think it is very possible to explain the full process scientifically, but nobody with the required understanding takes an interest in this forum, so we just bumble around. Just look here. I may try doing some calculations if I can manage to define all those variables.