My queen cell-builder/finisher is in a 5-frame deep nuc box, with a screened bottom and a queen excluder covering a front entrance hole. I keep four or five medium frames in this nuc, and use 1, 2, or 3 single cell bars, with as many as twelve cells per bar. I feed continuously with pollen substitute patties and feed a quart of syrup once a week. I like to keep the two outer combs almost solid with honey and pollen; the other two or three frames I maintain as combs of emerging worker brood, and frequently check for rogue queen cells (which I destroy and harvest the royal jelly for priming).
Using this cell-builder I've produced many groups of nice looking queen cells and some very nice queens. This photo is a group of my usual sized cells.
About a week ago I was between cell batches and had a comb of hatching eggs I needed to place temporarily, so I put it into the cell-builder, exchanging it with a nearly empty comb (one that was emerging brood). A day or two later I again swapped it with a fresh frame of sealed-emerging brood and placed a bar of fresh grafts. When I returned to harvest these finished cells, I noticed that all of them were uniformly large, larger than most of the cells I've ever grown.
I use JZsBZs push-in queen cell protectors, and my usual cells will allow the protector to be pushed all the way down onto the base of the cell-cup. These larger cells will only permit the cell protectors to be pushed to where the protector just contacts the rim of the cell-cups, and the tip of the cells are already protruding from the end of the protectors. In a few days, when this next batch is ripe, I will take a photo of these larger cells.
I am anxiously waiting to see how queens from these larger cells perform, and if they are actually larger, more fecund queens.