Great Question! Your LifeSpace / SIP garden functions through capillary action - "Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. " The problem is that in it's dry state, soil is actually hydrophobic, meaning that it will resist getting wet. So if you put a bunch of dry soil on top of even the most perfectly full water reservoir, no capillary action... it will stay dry. So to kick off that self-watering magic, thoroughly top water first until you soil is even and consistently moist - then your soil will want to stay moist, and will continuously draw water up from the reservoir to create the perfect growing environment!
In summary:
Install SIPs
Fill garden with container blend soil
Water thoroughly from top to kick off capillary action
Fill reservoir
Watch your garden thrive!