A first wireless device employs an uplink (UL) pre-transmission process to temporarily buffer data for processing prior to transmission of the resulting processed data to a second wireless device. To mitigate excessive delay of higher-priority data, higher-priority data is enqueued into the UL pre-transmission process without restriction (subject to capacity limitations), while lower-priority data is selectively enqueued into the UL pre-transmission process based on one or more criteria applied to a current volume of data in the input queue. Further, the first wireless device monitors the current transmission efficiency based on, for example, the current usage of transmission padding, and operates to dynamically adjust one or more of the criteria based on the monitored current transmission efficiency.