I think the difference is as a result of downloading a smaller file in case 1. In case 2, the combined effect of downloading multiple files is equivalent to downloading a big file.
In order to correctly measure throughput, you need to download a big file (eg 20Mb). Otherwise, the throughput will be fictitiously low. This is because the throughput starts increasing from zero(just before u start downloading), and if the file is small, it will finish downloading before you achieve the maximum throughput.
the reason for slow transfer at the beginning is that the system is being cautious : it assumes you have bad radio quality so it encodes the signal with high % of protection + it modulates the signal with a robust modulation.