You want it to fit correctly for sure, but the Eclipse (if I remember correctly) does have a way to tighten the back, just different then the new style. There should be two large 'tabs' that can be pushed towards eachother to tighten the helmet. For some reason I remember this always working better when the helmet was on my head rather than off (you should always tighten the helmet once on, but I seem to remember that the eclipse was difficult to even play with the tightening when it was off my noggin.)