  We present an investigation of the influence of structural distortions in
charge-carrier doped \lmco by substituting La$^{3+}$ with alkaline earth metals
of strongly different ionic sizes, that is M = Ca$^{2+}$, Sr$^{2+}$, and
Ba$^{2+}$, respectively. We find that both, the magnetic properties and the
resistivity change non-monotonously as a function of the ionic size of M.
Doping \lmco with M = Sr$^{2+}$ yields higher transition temperatures to the
ferromagnetically ordered states and lower resistivities than doping with
either Ca$^{2+}$ or Ba$^{2+}$ having a smaller or larger ionic size than
Sr$^{2+}$, respectively. From this observation we conclude that the different
transition temperatures and resistivities of \lmco for different M (of the same
concentration $x$) do not only depend on the varying chemical pressures. The
local disorder due to the different ionic sizes of La$^{3+}$ and M$^{2+}$ play
an important role, too.
