I don't like to think of myself as superstitious, but every time I find myself wanting to type something like "it looks like it will be just adding water from here on" -- I stop myself, like its inviting trouble. LOL Yes, the SIPs definitely simplify things.
Somewhere between 99-100% of the feeding happens during transplant. I put about as much dry time release nutes into the soil as I normally would during the whole run. That's how I've been growing for several grows, just dry nutes. I add them into the soil when I up-pot into their final pots. But, normally, when I flip to flower, and then again 4 weeks later, I top dress and add more nutes. So in my normal runs dry nutes would be releasing over time, especially each time I top watered. In addition to that, I tend to add Cal-Mag to most waterings (COB/LEDs and all), and tea, and occasionally Pro-Tekt.
On this run I said 99% because even though my plants haven't shown any signs of deficiencies, I tried to add some stuff anyway. I put some 2" PVC pipe through the top plastic (which in my set up I can't remove and replace easily) and about an inch into the soil, and I added a mix of liquid stuff I had on hand -- Botanicare Tea, Cal-Mag, and Earth Juice Bloom, and poured it down the tube. I put about 3 or 4 times as much as I normally would, and only put it in about 2 cups of water (per SIP). I did that at around day 25 of flower, and around day 39 I'll pour another cup or two of just water to flush it a bit. But that's just me making stuff up, no one suggested that would be a good idea. I've been told I'm a "belt and suspenders kind of guy", I over-build, I over-compensate, and often I do things that are totally unnecessary just so I feel like I've done all I can. I have no idea if there was any added benefit or if I was just throwing away nutes.
There is a lot of discussion about whether top-feeding SIPs is beneficial, necessary, misses the point... whatever. While I love to do experiments, in the end the primary objective is to squeeze the most meds from each run in the tent that I can. So in this case, I'm experimenting with one method of boosting the soil mid-grow. One interesting thing I've picked up, is that with SIPs the dry nutes can be very concentrated. The instructions that come with an Earthbox, for instance, show digging a small trench the length of the box and pouring in a continuous pretty heavy line of dry nutes, and then just covering it up. They don't mix it into the soil. What this implies to me is that in nature there are "veins" of nutrients in soil, and roots find their way to them and utilize them as necessary without getting burned. Which is why I am not concerned about adding stuff in concentrated spots. The plants will tap into it as they need it (apparently?).
Long answer to a short question.