Calling three medium frames of brood a 'garden hive' instead of a 'nucleus hive' seems like a distinction without a difference to me. Isn't what's in the box more important than what the box is? An 8-frame medium is the same volume as a 5-frame deep. Anyway, now that you know the exact size and condition of the little hives, what do you think about my questions?
I'm sorry I read that as 3 medium boxes. But if it is in an 8 frame box it is still a hive not a nuc.
There used to be 3 different sizes of bee hives above a 5 frame nuc, volume is immaterial, those were:
Canadian Imperial = 12 frames regardless of hive body depth
American Standard = 10 frames regardless of hive body depth
American Garden = 8 frames regardless of hive body depth
Those are the modern hive sizes, anything less than those frame widths, regardless of volume or depth, is a nuclei hive. That's the tradition of American Beekeeping, keeping the names straight helps in clarifying any discussion. Understand?
Lately I've been using a chicken waterer, with stones in the trough part to give the bees a place to land. Very few bees have drowned, they come to it in such numbers that the yellow jackets get crowded out and aren't a problem, and it doesn't seem to have set off any robbing (I put it on the opposite side of my house from the hives). I also like that I don't have to disrupt the hives at all in order to refill it. And I like watching them feed, too.
That is why you are not experiencing any robbing. Too properly feed with a community feeder it is necessary to remove the feeder some distance from the bee yard--at least 50 feet, the further the better. Using a remote community feeder will also stop robbing that is going on within an apiary saving all but the weakest hive that set off the robbing.
The best feeder I know of is one my brother and I devised. We constructed an inner top and then drilled 12 holes 2 7/8 inches in diameter in 3 rows of 4. Drill standard jar lids with 1/64 holes (12-24) per lid. Fill 12 Quart or pint jars with simple syrup, screw on the lids, and place in the 2 7/8 holes. Cover with medium super.
You can feed up to 3 gallons at once with a feeder that is pretty much robber proof. This feeder platform can also be used to feed fondant and pollen substitute by using 1/2 pint jelly jars so feeding can be done at anytime of the year without having to disrupt the bees within the hive.