Immersion RC LapRF 8-Way Event Timing Preliminary Operator's Manual page 6

Limitations
In general, you will find the LapRF to be truly best-in-class when it comes to RSSI timing systems.
The custom timing modules, coupled with a significant amount of processing power on-board, and
some highly refined curve-fitting algorithms , help to run races without an engineer present.
The one limitation that we will be very honest about is running the system in indoor environments
which are in the 'RF Hell' category.
Buildings with huge amounts of metal, roofs, walls, etc. are not only unsuitable for analog FPV racing,
they are a real challenge for RF lap timing also, and are best avoided.
6