Dominance Relationships of Genetic Mutations

A genetic researcher is studying a rare autosomal recessive disorder that affects the synthesis of a critical enzyme involved in carbohydrate metabolism. The disorder is caused by mutations in a single gene located on chromosome 5. The researcher discovers two different mutations: Mutation 1 (M1) is a 5-base pair deletion that results in a frame shift, significantly altering the enzyme's structure, while Mutation 2 (M2) is a missense mutation that leads to a single amino acid substitution in the enzyme.

Given that this disorder can manifest with varying severity, the researcher assesses the impact of each mutation on enzyme functionality, considering also the concept of incomplete dominance in heterozygotes. If individuals with Mutation 1 show a more severe phenotype than those with Mutation 2, what can be inferred about the dominance relationships of these mutations?