Which barcode scanner are you using Motorola's? If you are, their transmitters output power is around 100mW. Best thing to do would be reach out to your vendor and ask them to provide you with that information. You want to make sure there is no asymmetrical power going on between the AP and the client. Are you looking to deploy AP's with 2.4 or 5? Setting the power on the NIC to 25 to 50mW is something I would go with. Normally in Ekahau predictive I will set the AP's to 50mW this gives you some redundancy as well in case one AP goes down.
Success of warehouse deployment also depends on how you get the AP's installed in the aisles and how you setup the client profile. Hard coding the Motorola devices to use 5GHz if you are using 5GHz is a good practice if they switch between the two, it will interrupt user connectivity and if they are using telnet/ssh sessions they will get locked and will need to start all over again. Don't forget about the use of DFS channels if you are going with 5GHz. 1) not all devices support it 2) some support it but not by default such as Motorola 41N0 3) some support it but will require you to enable 802.11h in the controller. I have seen it many times where this was not considered and there were coverage gaps and everyone was suggesting to just install more AP's instead of finding out the root cause.
Also if you can drop the AP's 5' to 10' that helps but normally difficult because Forklifts end up hitting the AP's. I have used Cisco AP's with 2524 antennas and have been pretty successful. I have also used patch antennas, but that requires bit of a work and testing. Also pay attention of aisle width and rack width as well as what is going in those racks. Single rack vs double vs quad will show different signal loss.
If the aisles are longer you will most likely need to deploy two Access points in the aisles. Hope this helps. Feel free to ask any questions you might have.
