When evaluating buses using UBSC results, the LVF is still used although it is currently not noted in the software.
The System X/R at the bus is determined by the "ubSC_EquivZ 3P" attribute and used to compare with the Bus X/R. If the System X/R is higher than the test X/R of the bus, then the LVF is calculated using the bus X/R and the system X/R.