Jharii: Yah, lining up objects is a near hair-pulling experience, especially smaller ones. Lining up tilted ones is near impossible. Probably easier to do via editing .xml than by hand... I might try that next time I feel the urge to place some books on tilted tables, ugh.
One thing I found helpful in getting things to line up is play with the scale, rotation and offsets after you select an object but before you place it. I found I memorize the angel values better that way, and objects fall in line better too. Try that, maybe?
Here's Abbey of Izil being built:
And here are the actual .xml files:
Abbey of Izil
Abbey of Izil WIP
I'll try the Great Theatre next, if nobody minds .