Crumb question

Ok, I have been baking soudough for a couple months now, and while my loaves have been getting better and better tasting, the crumb has been consistently pretty tight, and not open like I wanted. On the weekend I finally got the kind of crumb I was hoping for! I think it was due to the fact that the hydration was slightly increased and I lowered my oven rack a little, but the oven spring was amazing and the crumb was beautiful. It was the first time I have actually seen the slashing direct any kind of rise. I am still trying to figure it out and try for an encore. I was so excited I tried again today, and got a kind of odd result. The outside edges had really beautiful open crumb, but as I got deeper into the loaf (I cut it in half to look at it) the crumb got pretty closed and tight. I am guessing it could be a number of things? Maybe underproofed, as I didn't do my normal proofing times because of the inconvenience of work ;). I retarded it in the fridge overnight, but I may not have bulk proofed long enough first. Or maybe the oven/stone wasn't hot enough yet? I used a different oven than I am used to so it could be inaccurate. Do any of these ideas seem likely, or is it just anyone's guess and I should try again?