The regulatory framework of pollutant emissions concerning non-road small internal combustion engines is becoming increasingly challenging. The upcoming scenario threatens to cut out small two-stroke engines because of the fuel short circuit occurring during transfer and exhaust ports overlap, causing the emission of unburned hydrocarbons and reducing engine efficiency. Despite this challenge, small two-stroke engines are unmatched in high power density applications in which weight and autonomy hinder the diffusion of electric technologies. The continuation of small two-stroke engines in the market will thus depend on the capability of mitigating fuel short circuit. From this perspective, some of the Authors found the low-pressure injection technology fulfilling the purpose at engine full load; however, in addition to system complexity and costs, a lack of mixture homogenization was noted at low load. Another solution concerns the adoption of a pocket milled in the piston skirt, connecting an auxiliary air intake to the transfer ducts by means of additional ports. This feature leads to the filling of the transfer ducts with fresh air only, reducing fuel short circuit during scavenging. Due to the fluid dynamic complexity, stratified-scavenging engines are typically investigated via experimental or CFD analyses, leading to high costs and times. In the present paper, a novel 1-D numerical approach for the study and optimization of a 55 cm3 stratified scavenging engine is introduced. The model, developed in the GT-Suite framework and validated through test-bench data, allows the replication of complex phenomena like air stratification. The effects of pocket volume, phasing of ports, as well as length of transfer channels, in terms of air stratification and fuel short circuit, is discussed in detail in order to provide design guidelines for stratified-scavenging engines and to find the best setup for the present test case.