In 1A coaches , berths are allotted at the tym of chart preparation. Its too difficult to predict whether u will get lower berth or not. Generally old age, handicapped people, pregnant women are allotted a lower berth.
Going for CK in the lure of LB is a suicide. Don't opt for it. U can talk to TTE, co-passengers ; moreover u can also make a formal request. Ask about it to local officials.