Cosmic rays are highly energetic particles from space. When cosmic rays hit the Earth's atmosphere, they produce a cascade of subatomic particles. A large portion of these particles are neutrons which can be detected using a neutron monitor either at a fixed location or shipborne. Shipborne neutron monitors have an advantage in that they can measure particles over a wide range of rigidity by conducting a latitude survey. In Thailand, we assembled the Changvan neutron monitor, a mobile NM64-type monitor consisting of three units of 10BF3 gas-filled proportional counters – only two of which are surrounded by lead. We made two expeditions (2018 and 2019 survey years) by sailing the Changvan from Shanghai to Antarctica and back. To study the energy-dependent effective area (yield function) of the Changvan leaded and unleaded counters, we perform a Monte-Carlo simulation in two steps. The first step simulates the interaction of the cosmic rays in the atmosphere and records the secondary particles that reach sea level. The second step injects these particles into a model of the detector with surroundings. Multiple atmospheric profiles are used to probe how changes affect the differential response function ($DRF$). We compare the simulated $DRF$ with data taken during the survey year 2019. We investigate and discuss the differences in the $DRF$ between the two leaded edge counters and the unleaded middle counter, all of which are inside the same reflector.