A semi-open space can be quite challenging.  There are several problems; 1) sound power is lost through open spaces limiting reference sound level, 2) As you fear, there can be excessive reverberation reducing focus and clarity, 3) Its more difficult for an acoustician to predict the sonic behavior for best seating and subwoofer placement, and other issues.  You question seems to focus on the second of the issues I listed.  For this problem there are only two solutions.  The best solution is to add acoustical treatment to reduce the reverberation of the room.  If that is not possible, the only choice is to reduce the number of listening seats and move these closer to the speakers, or the speakers closer to the listeners.  The acoustical principle is that the reverberation is too loud compared to the direct sound level from the speakers.  This is how focus and clarity are reduced.  Without treatment, the only way to increase the relative level of the direct sound is by listening closer to the speakers.  Turning the volume up is not a solution since the increased direct sound level will still create an even louder reverberant sound level.