So are you saying that you just took the trees out of their pots and planted the entire root ball on top of a tile? Kind of like the left hand side of the figure below? If so...you will not get what you want, as the roots will tend to grow down and then spread out when they hit the tile. When we plant trees in the ground on top of tiles, we work the roots, reducing the root mass and spreading the remaining roots out horizontally. They are then planted right on top of the tile, with just a little soil below (see right hand picture; the tile is represented by the thick line). This forces the roots to spread out horizontally right at the trunk base. Otherwise, the roots grow down and spread out well below the tree.
This is also why this is typically done in the spring, when it's safe to do a lot of work on the roots.
I usually also tie the roots to the tile with wire or rope to keep the plant from lifting itself off the tile as the roots grow.
Otherwise...I have found Korean hornbeam to be one of the slowest trees to thicken. Tridents can be pretty quick but it depends on your climate, soil, etc. Often trees don't grow much the first year as they build root mass, then they take off in year 2...but this is not a firm rule, some will explode with growth the first season.