Do you understand how NFL cap penalties are calculated? If Madden is at all close to real life in reflecting cap penalties, that's why it's different. Here's a simple example:
Sign a player, 3 years, $9m bonus, $12m salary.
Bonus money is accounted for over the life of a contract, so when you sign this guy, his salary is $4m/year for 3 years... and that $9m bonus is spread out over the life of the contract, so that player's bonus consumes $3m/year of cap room.
So his contract looks like this:
Year 1: $4m salary + $3m of bonus = $7m cap number
Year 2: $4m salary + $3m of bonus = $7m cap number
Year 3: $4m salary + $3m of bonus = $7m cap number
Now the reason the cap penalty changes, is because he is released before bonus money has been accounted for in the cap. If you release the player above in the first year of his contract, you should have a $9m penalty. If you release him in the 2nd year it's a $6m penalty, if you release him in the final year of his contract, it's a $3m penalty, but that's less than the $7m you were going to pay him so it suddenly becomes more reasonable to cut him.
Hope that kinda made sense, think I got most of that right. This is why in your example, you're in the final year of a contract, and it's a pretty straightforward cap hit. The number should vary over the life of it.