You're correct Doug. A similation will not tell you everything very accurately, but it gives only an idea. BTW, I am sure I could get closer to practical measurements by increasing the no. of reflection (as my room has brick walls) that I have quite ignored.
Here is another SIMULATION which made me decide not to chose the nearfield arrangement in the same room because I like a steep house curve.
I know there will be a dip around 30 Hz, but measurements might show that dip propably more or less enphasised with a propable slight change in frequency. But the concept is still the same...There will be a Dip with this configuration at a frequency low enough to be unpractical for a house curve without overstressing amps/drivers...
This is what I beleive to be the real intention of such room calculator programs.
