The one time that really stands out in my memory for wheel lifting was riding up Burke mt in Vermont. ...
The average grade of 12.7% for 3.3 miles makes this the steepest top 100 climb in the USA. BUT, those stats do not represent the true torture of this climb!! After turning onto the toll road for the last 2.5 miles it averages OVER 14% [I had 14.27%] to the top . That includes a “wall” about 1.2miles long at 22% followed by 16%”recovery” slopes. ....
I can only think of one time that I have had a front wheel lift off the ground when I was on a bike. A landscaper had put in a very steep section that was about 4 or 5 feet high on the lawn at a community park near a picnic area, and I pushed hard in a low gear to climb those few steep feet.
Otherwise when a hill is that steep, I am off the bike walking it up the hill. Like the 13 percent grade one below.
And as PDLamb noted, your body weight location is a big part of the center of gravity, on a touring bike we usually have longer chainstays so that puts your body further in front of the rear tire patch on the ground.