If a still ra follows an original kasrah in the same word, and no further qualifying condition applies, it is generally pronounced lightly. An original kasrah belongs to the word’s normal form, rather than being temporarily introduced for starting or linking pronunciation.
«فِرْعَوْنَ» — the still ra follows an original kasrah, so it is light.
«مِرْيَةٍ» — likewise, mim’s original kasrah gives light ra.
Three important circumstances need separate attention: temporary kasrah, kasrah in another word, and an emphatic letter after ra in the same word. They explain why apparently similar written cases can sound different.