That distance would be superb. Drifting between hives appears to be very much sub-species dependent - Carnies being much better at 'homing-in' than Italians.Would you consider 6-7 foot too close as in potential for future robbing, especially given 2 of them will be behind the active hive now which is an over-wintered hive?
A few years back I did an experiment with 8 nucleus colonies in a row, and found that 12-14" was the minimum spacing before significant drifting took place. That's spacing between entrance holes, not spacing between the boxes themselves. So - with an 18" wide box (which is our 'standard') - the boxes can indeed be touching - but only if they have central-(ish) holes, which is how I run them. With full-width slots (the 'standard' entrance format), they really need to be spaced apart by at least a foot.
Robbing - unfortunately - is quite independent of distance. Even spacing hives a 1/4 of a mile apart won't stop it. But - anti-robbing screens will - they're highly recommended.