DW1000 Preamble Data Rate

The DW1000 supports 3 diferent data rates (110Kb/s 850Kb/s and 6.81Mb/s).

I was wondering does the speed of the preamble change with different data rates. The EVK100 source code seems to indicate that the preamble is always sent at the fastest speed regardless of what the data rate is configured as

preambel only 16M or 64M