Resource Overallocation

I am re-hashing a large and complicated project and have started by programming in recurring meetings. I have set these up successfully and allocated the appropriate resources. The first problem I encountered was some resources showing as over allocated if meetings fell on the same day even though they may only constitute 2 or 3 hrs in an 8 hr working day. I overcame this problem by linking the meetings that occur on the same day finish to start.
I will though also need to allocate these resources to other tasks which will inevitably span at least one meeting and will also possibly overlap with other tasks. These cannot be linked as they need to overlap.
I have tried a test case where I allocated one resource a 15 hr task for which I have allowed him the whole of March to complete. This takes up 8% of his units and project has automatically programmed him to work 1.18 hrs a day to complete it but on the days he also has meetings he is showing as over allocated even though he is well under his daily working hours. How do I prevent this? Is there a way of running concurrent tasks without a resource showing as over allocated until he exceeds his 8 hrs a day?