The Influx Management Envelope (IME) is a tool for operational decision making when managing influxes in Managed Pressure Drilling (MPD) operations. There have been numerous developments to the IME in recent years, and it is gaining traction over the MPD Operating Matrix (MOM). Calculation of the IME can be done in different ways. The original approach of calculating an IME described in (Culen et al. 2016), give less acceptable influx sizes than using multiphase simulations. Some of this can be attributed to the used Equation of State (EOS), and some to the distribution of gas in the wellbore. There is ongoing work for creating purpose-built tools for generating IME's that consider the gas as a single bubble, but with a real gas EOS, as well as considering gas distribution. In this work, the sensitivity to the model used when creating an IME is studied. This is done through comparing the single-bubble real-gas IME by (Berg et al. 2019) with IME's generated using Drillbench Dynamic Well Control as well as the commercial multiphase flow simulator Ledaflow for synthetic test wells. Discrepancies between the results are discussed and the differences in the underlying model and calculation procedure with respect to the end IME is elaborated.