As I said earlier, this line of skimmers are notorious for overflowing, and it is due to the shape of the body, and too much air drawn. Putting the skimmer in the correct water depth, and restricting the air intake, is what makes these skimmers shine. The other mods are for your pleasure, not the performance of the skimmer.
Yes, that is correct. But you compensate by opening up the gate valve to lower the internal water level. If you want to avoid the calcium build up, plumb your air intake hose into your collection cup to draw moist air, and you will never have to clean it again. Here is a pic of how I did it to my Aquamaxx EM300. If you decide to do it, be sure to put the hole above the bottom line of the lid, so it does not draw anything other than moist air. See the moisture in the air line?