Unfortunately, during the winter (and also to some extent in spring and fall) the hives will be shaded on their fronts and sides, so the hives will be colder. A solid enclosure of that size, on all four sides will also make the interior area cool and damp, with poor air drainage year-round. Plus too hot to work in during the summer for you, when a breeze is what makes it bearable, even up here in NY.
I would rethink the plan. Having bees fly over your lawn is not a bad thing. (And you will adjust to their presence, as you get more experience dealing with them.) A single-sided barrier may be all you need to "lift" them up and away from a critical area, but preferably not on the south elevation where the entrance is facing. I would face them east, and put the barrier on the south, if that was the only solution. A wind barrier on the windward side does protect the bees during the winter.
But if you go ahead with it, you would need at least 5 feet, (preferably more) between hive surface (on all four sides) and the fence, for butt and working room. My own hives are about four feet from a row of 30-feet tall evergreens (on the north only). And I am always feeling crowded by that. I plan to move them out a couple of feet this year. I use all of that four feet and am always slapping the branches away from me.
Also a stand 30" tall will be very difficult to work. My own stands are about 12-15" off the ground (I am on a slope), and while this is far preferable than hives on (or near) the ground, it costs me extra effort in lifting boxes. And I usually stand on my solid-surface stand to work my hives. I can easily hoist heavy boxes up to about thigh-height, but from there to should height, any box weighing more than about 30 lbs is harder to control. Not to lift, but to move with delicate control needed to set boxes of live bees down carefully. I use a step ladder, and finally, late in the season a scaffold platform to work them. Bee boxes are heavy, my 10-frame deep supers can weigh upwards of 40-50 lbs, even after I have removed some frames.
Six hives in an enclosure of that size would not be pleasant to work, IMO. Six hives in a line would occupy at least 5' (end room on the line) + 1.5' (Hive #1) + 2.5' (minimum moving around space between each hive if you are agile and skinny), etc., + 5' on the other end. That comes out about to at least 30 row feet. I keep my hives just a bit less spaced apart (a bit less than 2') and I spend a lot of time walking around the line. Or temporarily heavy shifting hives to "collect" two intervals between three hives into one working space. It is not ideal. And then there's drifting...... Having the hives against the back wall of the enclosure (which is what it sounds like you're planning) and little space between them will make beekeeping a PITA. I would suggest having fewer, or finding another solution.
In the winter, I shove mine all together (with two, 1" pieces of foam between each stack to accommodate the the telecover overhang) and insulate around them in a block with 8' panels. (Eight feet being the standard size of a foam panel, and a group of five, 10-frame hives nicely matches that length.) This works well because I install the insulation very late, last thing before winter, usually in Dec., after my last OAV treatment of the year. However, in the spring it limits the ease of the early work because they are so snugly packed up. I keep the insulation on as long as I can stand it, just removing pieces so i can do the earliest inspections, and then putting it back on. And I keep it hand on the ground, ready for those frequent below freezing nights up here in May. I have spent more than a few nights re-installing it in the dark when a late weather report changes to an unexpectedly freezing forecast. Every year I plan to make individual insulation jackets for each hive so I can spread them out earlier in the spring. So far, I haven't got around to it. (And in the spring, I have no time for doing it, even though my motivation is high.)
I am curious about one thing, though. Is this your first year - six hives are a lot to start off with!
Nancy