Not feeding sourdough starter enough? I'm new to the whole baking thing, so I'm learning as I go along. In that regard, there may be a host of things wrong with my bread baking process, but I'm mostly curious at this point about my starter feedings. I don't really follow any rules aside from equal parts flour/water. How important is it to feed the starter in proportion to the starting amount? I've seen lots about a 2:1:1 starter:water:flour ratio or even 1:1:1, but I haven't really been doing anything like that. In most cases I just feed a static 40g flour/40g water each time; regardless of the starting volume, starter rises to double no problem and I make sure it passes the float test every time before I mix the dough.

I've baked 4 loaves unsuccessfully at this point, all have been flat with a large air pocket like this. My best guess is that this has to do with being under-kneaded but after doing some more reading I'm a little curious if there's any specific reason behind feeding a starter that much and if it could be contributing to my bread failures. Is my starter OK (i.e. I should look elsewhere to find the problem) or is this something worth changing about my process? Thanks!
My early sourdough loaves looked like that. Now they are less flat and have defined hikes through the crumb rather than a great interlinked cavern. 
The things that changed:


my starter became more mature and stable. It lives in the fridge and gets fed 2-3 times a week when I bake. I keep about 250g which gets 100g taken out and replaced for my standard loaf and 180 g on loaf-and-pizza days, plus another 60g at random times when my partner steals some. 
I’ve learned that in my kitchen a sourdough loaf takes a long old time to rise. Sometimes I bake it underproofed because that’s better than not having bread, but really mine needs 24 hours from start to finish. 
I gave up kneading. I read all the methods, watched all the videos... I slammed that dough down 300 times per loaf, kneaded for at least ten minutes, stretched and folded... and never got smooth elastic dough as advertised. Instead I got exhausted sticky dough that was a nightmare to handle and didn’t rise all that well. I’ve come to the conclusion that if dough has enough time it doesn’t require kneading. Now I mix the starter with water, mix in the flour with a rice paddle, mix a bit more about ten minutes later and leave alone for about 22 hours.  I might give it a poke if I’m bored, but that’s more for me than the bread. 
Shaping: I used to do a lot of folding/rolling up of dough before I put it in a proving basket for the last hour or two. Now I just kind of punch it down and gather it back up and dump it into a well-floured basket. 


I don’t have a current loaf to take a pic to prove my success (just back from Stratford, flying to Stornoway in the morning, had to actually do a discard feed for 1st time this year) but essentially my mantra would be ‘chill and give it time’.