Can confirm by extensive 464, 900 MHz, and 2.4 GHz radio field testing of products and test equipment for WAAS-like GPS data updates conducted c. 2000. 2.4+ GHz just doesn't play well with building materials, while 900 MHz provides the right balance of bandwidth and attenuation.

PS: It's not millihertz (mHz), it's megahertz (MHz).