Selective pressure.
As stated above, only homozygous are affected, considering the morbid allele given as recessive. More doubtful are the occasions when two or more alleles are set as morbid. When two of them are present (the individual is heterozygous) the software will not negatively select the individual. That could be but is unlikely. As a result, mortality rate will be underestimated when more than one allele is set as morbid.
A 50% value for the selective pressure parameters means a 50% chance for the homozygous to survive and be part of the next generation.
A 100% figure means no chance at all. The allele is a lethal recessive one.
With 0% the individual is kept whatever the genotype (no selection pressure).