I build a very simple coil. Generally 1.2 Ohm, 28 gauge, 2.5 mm and use a cotton wick. When I first build it, it will glow perfectly - center out. I don't get the thing more than a glow. When I go to carefully change wicks, it will never glow center out again. It is always hotter at one end. This is shown by a gentle pulse and one end will show hotter. Any suggestions or is this a normal thing?