Dynamically and partially reconfigurable architectures, like FPGAs, have increasingly become heterogeneous with DSP, RAM and communication interface blocks. However, in most of online FPGA task placement approaches, the FPGA is modeled as a homogeneous architecture. In this work, we propose a heuristic which focus on the online task placement problem on a multi-context, dynamically and partially heterogeneous reconfigurable architecture. Configuration Prefetching and Anti-fragmentation well known techniques are combined with the Place Reservation technique in order to improve resource usage capacity. Compared to a placement without reservation, our approach improves, on average, by 33% the number of placed tasks and by 46% the resource utilization rate.