So I think 3ft is more comfortable to work in. For three reasons. 1) I can do a wide stance deep squat with one foot on each side of the bed. It puts my center of gravity directly over bed and I can just bend over to weed. Then just shuffle my feet forward to work further until I’m done. 2) The average man can indeed reach into the bed at two feet from the edge squatting down or kneeling. But if your bed is 4 feet and you need to weed something in the middle of your bed at the two feet point you are more fully extended and don’t have as much strength or balance from that point. And your body will get more quickly fatigued with that reach.

Get a ruler and play with it in your house. Hold a pose at the various lengths you will need to reach for 30 seconds feel the degree of tension or relaxation. Choose the one that is more relaxed. I’m 5 feet 9 inches in height. If you are taller and depending on how much more then maybe 4 ft works. 

3) Wife and kids have a shorter reach than I do. I’m still the primary worker in the garden for sure but I’m a believer that things should be family sized. My shotgun is a 20 gauge with an adjustable stock. 

Obviously everything just depends. 😀