How near is near to each other with companion plants

[Llevrah]

Looking into companion planting with sq. ft gardening. Some things id like to grow are plant near to each other. I take this as in the adjacent ft square to it but can it be beneficial at any further distance from each other?
Also, when things like bush beans say keep away from onions how far away is away?

[Jungle Jane]

I keep things like peas & beans about 1 meter distance from my fruit trees etc so the roots aren't near the beans. Companian plants like to be side by side but beans & nasturtium can work if they're planted a couple of meters away from each other,the black aphids found my wall basket of nasturtium in preference to my runner beans last year. Some plants like a lot of water & some don't,when I was about to harvest my onions it was difficult to water the cauliflowers right next to them,I didn't want to water the onions. Brassica & sweetcorn like a high nitrogen feed,mixing these plants with tomatoes & peppers etc which like a high potassium feed can make fertilising difficult.