pingau lujvo

x1 places x2 in a horizontal position by reference frame x3; x1 lays x2 down

For "flatten" as in "remove lumps/bumps", see xulgau. See also pinpu'i, rajgau, rajypu'i.

In notes:

pinpu'i
x1 lays down/places down/puts down x2 in a horizontal position on/at x3
rajgau
x1 erects/raises/stands up (transitive) x2 by reference frame x3
rajypu'i
x1 sets up/puts up/places x2 in a vertical position on/at x3
xulgau
x1 smooths/flattens/levels x2