You can look up psychological research on gambling but the idea is to have the payout string along the gambler. If it pays out too often you get bored, if it pays off too infrequently then you get frustrated. I could see writing the algorithm to put little things in there like that if you wanted that sort of string along behavior. Casinos do it all the time in slot machines. But If I was under a deadline it makes the overall system more burdensome and less elegant. The incentive is to get it done and have people buy the game so taking the extra time is not justified.
With the understanding I have on the Dev team for this game (God bless their little hearts), they did not take the time to bake in all these scenarios into the code. They originally had a stupidly steep pRNG system and MUUUUCH later St. Bluke made the curve less steep as well as added some Chest score requirements into the 'of the Dragon' and Hakkon weapons.
There have been many theories thrown out since the dawn of DAIMP on how to improve your odds and this and that but they all amount to nothing more than magical thinking and reading patterns in a small set of statistics. Once the larger set is revealed you see that these are all anomalies and don't fit the larger set of data.
I've been through this a lot with my WoW experience vanilla to panda and done some brain time on trying to understand it. Game theory is cheap and people can actually tell (if only getting the feel from it) that the system is rigged to a standard set of drops. This could be okay if you haven't spent months grinding for a rare 1 in 15,000 rng drop (rng in rng). Games really have to offer a wider range of drops that are all rare but all offer something unique. DAIMP i don't expect much from as it's basically a tacked on part of the DA SP, which means I enjoy it as my expectations are low and it beats that bar for satisfaction. I don't really even care if i don't get a hakkon, as long as i'm having fun. That said, if DAI was solely a MP game, I would feel let down and possibly ripped off. More drops would be required, more maps (lots more and much longer/bigger as to take hours to get through with rewards scaling to the time the party stayed in and didn't have a player leave (granted the health implications of that). Anyways, i don't expect a lot and don't see myself staying on if all i'm doing is grinding for some particular elusive rng item.
Perspective from my eyes, I spent half a year girding rep to get a special faction only mount in WoW only to have Blizzard turn around and make the grind time weeks before i finished... I have learned to not invest time into any particular one thing because it can be changed at the whim of a developer. I like hard achievements but only when the integrity of the system is reliable AND fun. Not comparing Bioware to Blizzard, but these things can be arbitrarily changed by corporate decision makers. EA could decide to shut down access to DAIMP and make players re-buy yhr MP only (maybe with 1 or 2 new maps) for their new console. I could see them doing that to the ME3MP.
Long story short, go enjoy your game, if the drop comes great, if not you still had fun. Grinding (for RNG solely anyways) is no fun and risky business.