@Buds Buddy do you have aeration in your sohum/org soil SIP? I really think a 60/40 mix will make a big difference. I know that limits space for the bulky nutrition we feed organics and LOS, but I think over a few grows we can work it out. Certainly spiking with some geoflora, even for LOS, will get us most of the way there, but I think our gained efficiencies will impact positively also. Compost etc are a challenge in SIPs - aeration, aeration, aeration.
Too late, I know, but consider (real seriously) next time a major aeration addition into the org soil with lava or perlite and I think it will take up a lot more fertigation side by side. Sorry I wasn't clued in to help from the start.
The reason is that you're hitting field capacity too easily in too much of the soil. With the org soils, usually, they have less aeration and more bio-matter which has to be counter-acted in SIPs. You prob have field capacity-plus for a few inches at the bottom. Aeration will help sort this. Cloth pots help a bit too but a serious aeration increase will help this issue and start moving fertigation through the system. I tested this out in a 27 gal test-bed only, and with org. tomatoes, and it really sounds exactly like you are seeing what I, and many others have, with org soils. Consider too, the surface area lava and/or perlite provide for microbes is about a football field's in a couple of cups worth so its great for organics.
I actually culture bennies in a lava-stone/perlite-only bed (in a 10x20 tray, in a fishtank, with an airstone buried in middle so things don't get scary in there) that I harvest from for every seedling and transplant.
After the fact I can't think of a huge amount to help you. I know it sounds weird, that, "we need to dry your soil out to get it to use more liquid" but that's the real deal.