The higher the power, the longer the range would be. Need to check if the correct antenna is being used. If the problem is portable to base, then it could be due to a transmitter problem, and if it is base to portable then it could relate to a receiver problem. VHF offers two types of antennas, 9cm and 14cm. The longer antenna will provide a higher gain and longer range.
Emphasis is a type of audio shaping a noise filter.
Both the transmit and receive radios must have this feature turned on for proper operations. If either is turned off, then there will be poor audio clarity, which can be construed as a range issue. At maximum volume, LLE can degrade the intelligibility. This kind of problem usually exists in high noise environments. Again, intelligibility can also be construed as range issues.