There has been alot of discussion about this issue especially with the increase in rack power densities. Trends have been shifting from typical 20t CRAC blowing air either undrfloor or blowing up to "above isle cooling" and even cool rack solutions. To address your problem(s) though, is this an adverage reading across your facility or is it just in one specific area? Where you are getting this reading, how are the racks pouplated? I agree, racks closer to the air unit recieve , sometimes, less air than racks father out. Obvously, you facility must be getting denser (rack quantity / w per sq ft - sorry meter mate) thus the upgrade. You could have a simple soultion such as adding additional units or it cold be a more complex one. Check out your power loading across your PDU's and compair it with your temp / air movement reading. You can change readings just by rack placement. Just some quick ideas, we do case studies like this all the time. There's alot of good information and white papers on this subject. Good luck