Are U sure that configuration is OK? because it is weird.
All i know is that after defining TRX as HR capable, enabling HR on cell level and defining half rate threshold , the cell began taken HR traffic ( of course according to threshold and traffic load).
Why don’t you test it by setting the speech version thresholds to zero for half rate triggering, in this way only half rate TCH will be assigned on this cell, as may be there isn’t enough traffic on that cell to trigger half rate.