The spontaneous packing parameter and the bending rigidity of small reverse aggregates similar to reverse micelles in different diluents have been investigated. The considered system consisting of a common extractant (DMDOHEMA), a lanthanide salt (Eu(NO3)3) and water in various n-alkanes (n-heptane, n-nonane and n-dodecane) has been studied using molecular dynamics simulations to the obtain penetration behavior of different diluents. Umbrella sampling and fluctuation theory have been used to yield the bending rigidity. Different approaches for the determination of the packing parameter have been applied. For the most reproducible methodology a spontaneous packing parameter of 4.6 and an effective rigidity constant of 50 kBT per extractant molecule has been found.