Armagh1, condescension not withstanding, CJoseph is 100% absolutely correct. To add, because he won't, has probably done more surveys and active installs in hundreds of Fortune 500 companies around the world, and is one of our company's leading SEs in terms of best practices.
We (Aruba) recommends you set the AP power at the power the least capable/least powerful device you expect coverage with when doing a survey. If all of your clients are 100mW clients, then set that as the modeled adapter in AirMagnet, then you can set the AP power at 20dB and do your survey. If your least capable device is an Intermec CK61G HHT, with a transmit power of 20mW, then set the AP to 13dB power ouput, set the modeled adapter in AirMagnet to that type of device, and do your survey.
As I'm sure you know, coverage models and capacity models are two different things to plan for, but the coverage model still has a baseline of minimum coverage and that is what we are discussing here when setting the AP power to match the client type. We also recommend to set min and max at the same value such that the AP power is constant and won't change. Having a fixed power ouput of the AP(s) being surveyed with is a requirement for the survey to be valid. If one is at 12 and one is at 15, unless accounted for in the model, the survey will be invalid.
It is NOT good practice to rasie power of the AP *just* to get a bigger coverage model unless you are accounting for the clients that will be connecting to the AP, or the minimum SNR at the client is lowered. While higher output of the AP will give bigger coverage model, the client 'reach back' is the same (as clients will not raise power nor will the APs become MORE sensitive at higher AP power ouput, the client xmit and AP rx is a fixed link budget).
Best practice is to set the coverage threshold based on the client types to be used and the applications required (generally -65 for voice, -75 for basic data), identify all areas on the floor plans that require coverage at or above that threshold, and design accordingly. The environment (propagation and fade margin models) will take care of itself such that in an open warehouse you should get better propagation and fade margin than what you would find indoors. If you just raise the AP power up to get a bigger coverage area, the clients may not likely be at or above the threshold due to the longer distance and lower client power ouput to reach back and will fall below requirement at the edge of coverage.
That is the best practices put forth in said documents CJoseph refers to. If you need the max power ouput for the APs you will be modeling, they are and always have been on the data sheets. Power range is anywhere between 0dB and max. Our user guides are not behind a paywal or login and can be read for details on the how-to or the granularity of the power range (0.1dB for newer code, 1-3dB on older code depending on version).