RDWC Control Reservoir

What size should the control reservoir be in relation to the plant buckets? I've heard people say it should be larger, not sure by how much, but I see a lot of rdwc setups on Youtube with a 5-gallon bucket setup and a 5-gallon reservoir. Hygrohybrid actually uses a much smaller reservoir than the size of his buckets.

I was curious to hear your input and why you feel that is the case. Thanks

Res size depends on setup. Is res outside? Is it outside room? R/O? Temp? Decent aeration should be a factor as well. I (personally) use a small control bucket that mixes everything, same idea as undercurrent setups.