Tafkhim is the prescribed full or heavy resonance of a letter; tarqiq is its prescribed thin or light pronunciation. Neither term simply means speaking loudly or quietly.
The lam in the name Allah is pronounced heavily in some positions and lightly in others. For ra, the reciter must examine its own vowel and, in certain cases, the neighboring letters and the nature of a pause.
Compare: In «قَالَ اللَّهُ», lam in Allah is heavy.
In «بِسْمِ اللَّهِ», the same lam is light.
Its point of articulation has not changed. What varies is the prescribed phonetic quality.