and likely not having seen the UA or W/S symbology as it changed to non conformal other than in the sim
Indeed.
When the actual flight path is below the HUD FOV, i.e. performance decrease W/S situation, with pitch attitudes within the conformal range (normal non UA display), the FPV remains visible at the very bottom of the HUD FOV and is 'ghosted', i.e. a dashed line symbol. The 'solid' HUD W/S steering ball still provides W/S guidance relative to the ghosted FPV.
I have observed various levels of confusion in this situation even with reasonably experienced HUD drivers. These transitions out of and back into the normal day-to-day conformal display require some degree of practice. PFD is the fallback.