ceiling model material for Cara?

I am trying to get the baseline model for my listening room set in Cara. As some of you who have used this tool know it is sometimes difficult to pick the material from the list that best approximates what you have in you room. What have others used for the best fit for your average drop ceiling tiles. Mine are made by Armstrong, that's about as much as I know about them.

I'm not sure if the Acoustic Board material model is correct for the ceiling. If it is, I have a lot of work to do in the HF area!
There could be a couple of things going on. First, just from looking at the description in CARA my guess is "Acoustic Board" is not the right material surface for modeling a drop ceiling, though not too far off. To get it just right you might have to build a custom surface. A little research on the Web or a call to Armstrong should provide the necessary info for building the right material surface. A quick example of the info available can be found here http://www.controlnoise.com/ceilingtile.html.

Also, what speaker model are you using? If it is custom it may need tweaking to give a true representation of the speaker's output. For instance, I made a couple of mistakes initially that when corrected made a significant difference in the results. One was using the overall diameter of the speaker instead of the rubber surround. CARA wants the measurement of only the "effective membrane surface".

Another mistake was using the rated efficiency for my 4 ohm speakers which was 2.83 Volts/m and not the 1 Watt/m spec CARA wants. It was also necessary to change crossovers to get a more linear SPL.

BTW, these recommendations came courtesy of ELAC Technische Software themselves. Their support, what little I've needed, has been excellent.
I would suggest that it's pretty far off. The peg board has a mid band absorption quality and quite a bit of diffusion, the dropped ceiling produces a big bass sink and high frequency absorption. To model this correctly you need to put in the sub floor (above the dropped ceiling) as the true ceiling, then add the ceiling tiles as a "hovering" layer below them. You should not use any of the things that CARA has in their database, but rather get the data on the ceiling tiles and use the material editor to build that material. If you don't know the data on the ceiling tiles I suggest getting a copy of the book "A compendium of materials for noise control" It was published in 1980 by our government and is out of print, but many libraries still have a copy. It will give you the absorption coefficients for just about any material at a variety of frequencies.
Thanks for the tips. I am only using the room ambiance tool for now to try to get a handle on what treatments would be most effective. I reran the sim using Rives suggestion about treating the drop ceiling as a hovering abject and the results where very different in the low frequencies. So it seems that I have a huge bass trap over my head as well as a good amount of HF absorbancy. That does match what I hear, not much spaciousness to the image.