Verma modules of superconfomal algebras can have singular vector spaces with
dimensions greater than 1. Following a method developed for the Virasoro
algebra by Kent, we introduce the concept of adapted orderings on
superconformal algebras. We prove several general results on the ordering
kernels associated to the adapted orderings and show that the size of an
ordering kernel implies an upper limit for the dimension of a singular vector
space. We apply this method to the topological N=2 algebra and obtain the
maximal dimensions of the singular vector spaces in the topological Verma
modules: 0, 1, 2 or 3 depending on the type of Verma module and the type of
singular vector. As a consequence we prove the conjecture of Gato-Rivera and
Rosado on the possible existing types of topological singular vectors (4 in
chiral Verma modules and 29 in complete Verma modules). Interestingly, we have
found two-dimensional spaces of singular vectors at level 1. Finally, by using
the topological twists and the spectral flows, we also obtain the maximal
dimensions of the singular vector spaces for the Neveu-Schwarz N=2 algebra (0,
1 or 2) and for the Ramond N=2 algebra (0, 1, 2 or 3).