They seem to be unable to sympathize unless they have had same experience. For example:

ILI *calls to inquire if I'm going to a certain formal event*
me: sorry no, I'm down with flu, would rather spend the next 2 days in bed
ILI *tried to persuade me how important the event it*
me: no, I'd rather rest now so I'll be ready for work next week, it's chilly outside and there will be parts where we'll have to be sitting outside
ILI *pushes further, explains how I can avoid all those parts where we'll be sitting outside in the breeze and drug myself up*
me: *scratching my head, wondering why he isn't picking up from my intonation that I'm about to lose my voice too as I'm half-whispering on phone*

Some time later me this ILI and myself driving in same car:

me *starts coughing*
ILI: you're coughing too? I had this cough for 3 weeks *proceeds to deliver a sympathetic mini-speech about coughing*
me thinking to myself "oh ... I see how it works"

Seems like when you're telling Fe-PoLRs about how you feel, they can automatically discard this information as bullshit and may be even suspect that you're just pretending or trying to trick them into something. This doesn't mean, however, that information is indeed false. The times that they do show a response to Fe-information is if they have processed it through their Fi at some point, such as the cases where they personally can relate.