The more important neutronic characteristics are simultaneously analyzed in the context of fusion-fission blankets. The analysis is referenced to a gas protected cavity, where dimensions and material compositions are varied. It is intended to know the regimes in which that hybrid blanket works when two independent variables are changed. The 6Li enrichment and the atomic density of 238U have been selected as those variables, and the study is performed for two different solid breeders Li2O and γ-LiAlO2. The effect of the thickness of the fertile zone was pointed out in previous articles and here we look for an optimum working point and will set a comparison with precedent results when LiH is used as the solid breeder. A physical figure of merit is established, which relates the characteristics of the fertile zone. Constraints on the TBR and fissile production are introduced to obtain efficient working points. Finally, the He, liquid lithium and Li17Pb83 eutectic are considered as candidate coolants and their effects on the neutronic performances are analyzed.