If the coverage area is larger than the area you are using the humidifier in, this is no cause for concern. The humidifier may even work better than intended, as it won’t have to humidify its maximum coverage area. You may be able to run it on a lower speed or for shorter periods of time to achieve the results you want. The desired humidity level won’t be surpassed since most of the machines turn off when the RH you set is reached. If your machine doesn’t boast this feature, get a humidistat and watch the RH levels carefully.