Joe Friel’s work is definitely not going to jive with the UA methodology. Friel’s Fast after 50 has its central tenet that HIIT is required for the aging athlete, you won’t find that in UA plans until later in each training cycle.
These are competing methodologies, you have to choose one and experiment. UA is more Maffetone related with “low hanging fruit” being the terrible base aerobic conditioning we all have which can be improved with mostly Z1/Z2 work. Once that is accomplished, you layer onto some more higher zone work to fine tune your fitness.