I dont believe that there is any ‘minimum’ amount of space persay, just keep in mind that you do want their to be sufficent air flow going to and from the victors, i am assuming your refering to the muffin fans on the victors. I have cut it close in the past, probably around 1/2" but i dont know if i would recommend it again, with that sort of clearance you run into other problems other then just air flow, like the amount of effort/time it takes to access things and change out parts, tighten connections, change connections, running wires, these sort of things are also things you want to consider when determining the amount of clearance around components.
But to answer your question more directly… as long as there is sufficent air flow, and the components wont over heat, i’d say 1/2" is fine, but not ideal.
Half an inch is plenty. The truth is that our Victors only rarely get hot enough to warrant the use of the fan. By the end of the match, I suspect that Victors running drive motors with out fans would be a little toasty, but probably not near failure. This is a bit like the case of putting heatsinks on motors- it helps in the long term, but over a two minute match, it’s not really effective. Cooling the Victors shouldn’t be a huge factor for us, as long as the fans are running, the Victors will be more then adequately cooled (which is why they are there- so you don’t have to ever worry about them overheating do to poor airflow).
Bigger considerations in my mind with a tight clearance like that is going to be accessibility and visibility.
1/2" should be OK if the controllers are not close to each other. If they are packed in tight you might want a little more than that. Remember that if they are too close, then the air the fan pulls through for cooling is actually it’s own heated air coming back. Like recirculate on your car, the air just gets hotter and hotter.