When ra itself has kasrah, it is pronounced lightly. The presence of a heavy letter elsewhere in the word does not automatically cancel this clear rule.
«رِجَالٌ» — the initial ra has kasrah, so it is light.
«رِزْقًا» — the ra remains light despite the later heavy qaf.
Remember the basic three-way distinction:
رَ — heavy.
رُ — heavy.
رِ — light.
This applies to a vowelled ra. An unvowelled ra requires an additional look at the preceding sounds and certain exceptions.