Iron Flask Drop Rate Is Bugged, or Missing Decimal Points

I farmed expedition for 3 days straight, got 678 exotic coins, dropped nearly every expedition unique, but have not found 1 single iron flask (the normal/magic flask).

My friend farmed expedition for 3 weeks, dropped 5 unique iron flasks, but only dropped 3 normal/magic iron flasks.

Iron flask (normal/magic rarity) should not be more rare than the unique flasks. It should not be more rare than Valdo's Puzzle Box (I dropped multiple in the last 3 days). It should not be more rare than Mirror of Kalandra. You should not need to farm 1 week nonstop to drop 1 normal/magic rarity iron flask.

I suspect the Iron Flask drop rate is bugged, missing a decimal point somewhere, or something like that. The drop rate of this flask must be increased.