Can you provide a little more info like how many MR's, how big of an office space? Multiple floors? Ceiling height? Is there a lot of neighbor interference? Are you using both 2 and 5Ghz?
In very general terms you may just need more MR's closer to your clients and with lower power settings. You might also be able to adjust minimum bitrates to try to get clients to roam better. All Ap's have more or less the same radio transmit power since it is regulated by the FCC (or your countries equivalent) You may also consider getting a proper site survey done or at least a predictive survey to help understand better what is needed to meet your requirements.
- Ex community all-star (⌐⊙_⊙)