for what I experienced... 'seating' a tire can take quite some pressure... I though 60 - 65 lbs (on 700c 38mm) would be enough... turned out I was wrong.
I had to get the pressure up to 85 almost 90 lbs to get the tire seated properly - left it that way for 20 min. and then brought the pressure down to running psi.
Rubber is 'sticky' and without some excess air pressure, the tire may seem as though the bead has 'seated' properly, but the rubber resists... the extra pressure assures the tire is properly against the sidewall.
28c would prolly take a bit more pressure to seat...
when I hand spin the tire, I do a real slow spin, and as tire rotates I move it from vertical to horizontal, back and forth, to both sides... sealant is viscous and takes a while to get around...
just my experience with 2 different wheelsets and tires...
Ride On
Yuri