Underfermented or just right?

Hello, bakers!

Since my last post I was continuously working my way towards more open crumb. My last two bakes were by Kristen Dennis basic open crumb sourdough recipe. Fist one (at 80% hydration) was hopelessly overfermented (I didn't use aliquot jar ) and turned out flat and dull. With second one (78% total hydration) I used aliquot jar monitoring and let it go up to 60% increase in volume in the jar (folded dough itself was maybe 40% or so), then I shaped and proofed further for 30 min before putting to super cold fridge overnight. 

This loaf had some oven spring, an ear and even the most open crumb I've ever got. But although it doesn't have much compressed crumb, it has some cavities, that might be mark of underfermented dough... Today I'm going for the third try and could use some help and expertise from you - is this loaf underfermented? Shall I push a little (or maybe much) further or it looks just fine and cavities/tunnels are from faulty shaping/not enough degassing? 

Really looking forward for your opinion!

Olga :)