My Regency insert has a very small firebox. I was wondering if there is a general rule of thumb as to what size splits should be for best operation. Whether e/w or n/s , how much free space should be on the sides to the edge of firebox? I have noticed when e/w the longer splits when real close to edge, makes the smoke and flow swirl out and around the left side of the split. My insert will accommodate 18", but I thought I read somewhere to make them at least 3" shorter if not more. How and will this affect the burn, and also can this have any affect on glass hazing up quicker than normal? Thank you.