How many frames per box? If 10, it sounds like the bees need an extra box since they usually don't build comb between the frames and the lid till the frames in the main box are full. If you don't have all the frames drawn, you might check the spacing between the frames. You can run as few as 8 frames but they need to be drawn comb. When you are drawing comb, use 10 frames for the best result. If you give them too much space, they can be pretty creative. You may just have a little bridge comb holding the frames together. If conditions aren't just right (i.e., a good nectar flow) for drawing comb, they will start comb sideways to bridge the frames. If that's what you have, just scrape it out as clean as possible and let the bees try again. If you feed them 1:1, or even thinner, it will encourage them to draw comb so feed if they aren't bringing in much nectar.