Bhí sé 'n a shuidhe ar a ghroga. = He was sitting on his hunkers. (or on his heels). Bhí sé ar a ghroga os ceann na tin = He was crouched over the fire. Bhí an madra 'n-a shuidhe ar a ghroga os comhair na tine.
ar a ghroga = on his hunkers. Bhí sé ar a ghroga ag an tine = He was crouched at the fire. Bhí an madra 'n a suidhe ar a ghroga os comhair na tine = The dog was sitting on his groga in front of the fire.