Does lower lv urns give as much chance as the higher lv one for black ibis pieces? I already got camouflage and lotd.

To the best of my knowledge (though it's possible I may be mistaken), all levels of urns are equally likely to grant a piece of ibis. However, the sarcophagi and chests have a better chance, making an optimal strategy to check only those in the lower rooms, then go through as much as possible in the highest two rooms that are accessible at your Thieving level.