I would recommend also giving stretches for the SCM, pec minor, and possibly Butler nerve glides for the UE. Anything that has adaptively shortened takes awhile to remodel.
My question is always why did this occur? Obviously no one wakes up1 morning and out of the blue develops a syndrome. Are there shoulder issues or blocked cervical movements that the person is compensating for ? If there is a mechanical issue in movement that produced this it has to be treated also. Can the peripheral Sx be produced is sitting with the affected UE resting on a table to place the nerve roots on slack. If so there are most likely other sources o neural impingement. Just thoughts to ponder.
If after a month they are abolished with regular stretching it needs more aggressive ( harder, longer) or look around the cervical spine