Maybe it has something to do with the staking? I think you are also staking on long term deposits.
Considering the deposits were made within minutes of each other, there really shouldn't be any difference. But that's just my personal understanding. Hoping someone better would come along and enlighten me
Bear with me I'm not always the best at explaining things but let me give it another shot.
To make things "user friendly" we typically will describe "term deposits" in terms of a length of time such as a day, a week, 3 months, etc. This makes it quick and easy to relate to how long the term deposit is.
So one might say I am going to term deposit 100 coins for a week, or I am going to term deposit 1000 coins for 2 months. Even the wallet interface is designed to be used in this fashion.
So in terms of thinking about, talking about and even doing a term deposit our mind is on these time descriptions. Now the code is actually much different indeed. First thing to grasp is that the code can't think but rather executes a set of instructions. These instructions are static and unchanging. Whether the code executes once or 500 times whether yesterday afternoon or right now it does the same thing each and every time so that piece of the puzzle is static or even we could say carved in stone.
Now let's start thinking like we are this code. The code is to execute a block on the blockchain every two minutes. The code also has the authority and ability to variate from that two minutes as it deems necessary. This occurs more specifically as the MIDAS algo monitors the ongoing and changing amount of network hashing power. As network hashing power goes up or down the MIDAS algo will respond and this response includes making adjustments to the difficulty level and even the block timing. This is necessary to provide additional blockchain security for the coin which is yet another discussion topic. Suffice it to say the 2 minute block timing is subject to not be 2 minutes. In fact you may even note an error being reported in the console for "getmininginfo" stating that the expected number of blocks in the expected timespan was off by some margin.
Now let's start assembling these different pieces together. While we think of a term deposit as 1 day the code actually thinks of that as 24 hours x 60 minutes or then 1440 minutes divided by 2 minute block timing = 720 blocks - so then when you think 1 day the code thinks 720 blocks. Herein we begin to visualize discrepancies. This is because a day is unchanging at 1440 minutes but a sequence of 720 blocks may or may not be 1440 minutes because the 2 minute spacing interval is dynamic and ever changing.
Now digging deeper. When you clickety-click doing up a term deposit the only thing the code can do is take a "snapshot in time" and then calculate and spit out an amount. While at the point in time this occurs it's accurate.. moving forward it becomes wrong. You see the code is shooting at a moving target with fixed parameters. The code is fixed and static and yet at the same time it is making calculations based on variables that are fluid and non-constant.
Here is an analogy. The police officer shoots a speeding car with radar and the radar guns says the car is going 100. Assuming his gun is accurate at that snapshot in time the car was in fact going 100. A few hundred feet later the car slows down and is now going 80. The radar gun report of 100 is now no longer accurate because the speed of the car has changed since the radar gun took it's snapshot and calculated 100 mph.
Rest assured there is no reason for alarm because you detect a mismatch between expressing lengths of time vs. a moving block chain whose timing will vary. If you prefer consider this option: When you do a term deposit stop using time elements and start using blocks. In other words term deposit 100 coins for 720 blocks or 1000 coins for 21600 blocks etc. Then you and the code will be on the same page but don't forget even if doing a term deposit in blocks quantity you are still going to face the fact that those blocks are not going to crack like a swiss watch at exactly 120 second intervals block after block.
One other thing... as quoted, "Considering the deposits were made within minutes of each other, there really shouldn't be any difference."
My response to that is "within minutes" matters and there can be a difference. Any of the variable components could potentially change within minutes thus creating different calculated outputs.
I appreciate your digging into this coin and wanting to know it inside out. Be patient and bear with me and I'll always do my best to provide any information you desire.
If this is still unclear let me know and also let me know which part of this doesn't click....