Veja CMR.

names(trellis.par.get())
trellis.par.get()$layout.heights$strip

bwplot(resposta~preditor1|preditor2,
       strip=strip.custom(
           factor.levels=c(
               expression(atop(italic("P. paradoxa"),"outra info")),
               expression(atop(italic("H. raniceps"),"outra info")),
               expression(atop(italic("P. azurea"),"outra info")))
       ),
       par.settings=list(layout.heights=list(strip=2.5))
       )

À disposição.

Walmes.