The Trans-Iron Galactic Element Recorder for the International Space Station (TIGERISS) is designed to measure the abundances of the rare ultra-heavy Galactic cosmic rays (UHGCRs) $_{30}$Zn and heavier, and is planned to launch to the ISS in 2026. TIGERISS uses planes of crossed silicon strip detectors at the top and bottom for charge (Ohmic side) and trajectory (strip side) determination and acrylic and silica aerogel Cherenkov detectors for velocity and charge determination. Following selection in the second NASA Astrophysics Pioneers Program call, instrument configurations are being studied for available ISS external payload accommodation locations on the Japanese Experiment Module (JEM) ``Kibo'' Exposed Facility (EF) and the European Space Agency Columbus Laboratory (SOX). Expected UHGCR observations are modelled using differential geometry factors determined for detector orientations within the geomagnetic field over the ISS 51.6$^{\circ}$ inclination orbit to determine geomagnetic screening. Energy spectra are integrated using the higher of the energy needed to trigger the instrument as a function of incidence angle determined by Geant4 simulations or the energy needed to penetrate the geomagnetic field for time-weighted bins of geomagnetic latitude, instrument orientation, and incidence angle. The expected abundance measurements are reduced by the fraction of events calculated to fragment in the instrument as a function of incidence angle.