The sim on question is available for purchase on the Internet. It is a very interesting game and allows the player to try all sorts of tactics in all sorts of environments with all sorts of aircraft and all sorts of weapons, etc, etc. It costs about €80 and is a beautifully designed piece of software.
It models the aerodynamic performance (not the aerodynamics) of the aircraft, their fuel, number of weapons and such.
It models missile flyouts.
It models loads of stuff and makes me think I could spend a few hours on a rainy Sunday afternoon running loads of engagements against my favourite enemies with a glass of wine in my hand.
IT DOES NOT model the full 3D RCS of all players dynamically (or in any way really, given the availability of such data, not to mention their sensitivity). It does not model missile datalink during flyout, exhaust plume interference, differences between skid-to-turn and Roll-to-turn, command link roll off due to the position of the missile relative to radar scan, anaprop..... And that's just stuff during post launch command and guidance.
So what assumptions does the simulation make? A single RCS figure for and aircraft based on "it's the size of a marble"? I don't know. But I can promise you all the dynamics of an active, long range, radar and command guided missile are NOT modelled in this simulation.
So how credible is it? If you are simulating this type of engagement with the above limitations, not very.