Sharing a broad region or an exact articulation point does not make letters interchangeable. Their distinguishing qualities also matter. Practise these contrasts:
ق / ك: different places in the rear tongue.
ء / ع: different throat regions.
ه / ح: distinct throat positions and sounds.
ط / ت: same point, different qualities.
ظ / ذ / ث: shared point with distinct phonetic properties.
ص / س: related region but emphatic versus plain sound.
Produce the sounds separately before comparing them in words. Establish accuracy before increasing speed.