Horizontal Cracks

I've been trying some rye sourdough recipes from The Rye Baker by Stanley Ginsberg but most of my attempts have these deep, horizontal cracks in the loaf. This latest attempt in the picture is the GOST Borodinsky. (Flour: 65% medium rye, ~19% bread flour, ~15% coarse rye meal. Water 80% (I decreased this from 100% hydration), Salt 1.3%. Red Rye Malt 6.2%. Molasses 5.5% and Coriander 0.5%). My kitchen is about 65 F this time of year and drafty. My guess is that the dough is underproofed  and that my chilly kitchen is slowing down the starter. I'd love to know if that sounds right or if anyone has other advice. I'm fairly new to rye bread. 

image2.jpeg