The calculator assumes a linear-return as the number of days progress towards the calculated Future Price. In reality, as that price is reached, the underlying fees generated have increased in value.

Take note here:
1 day position = $0.94 return
200 day position = $187.53 ($0.94 * 200)
In reality, the position would be generating MATIC and USDC, where MATIC is increasing in value. So a linear return isn't the ideal calculation here.
When the position of days is increased, I would expect to see the return of MATIC and USDC increase rather than stay the same - that way it could factor in increase in value.
Simpler way to view this problem
It's easier to visualise if you increase the Future price to be something extreme like $500 in future, across a 200 day position:
Take note of 1 day position, $0.94 yield, $1.5 future price

Take note of 200 day position, ONLY $187.53 yield, yet $500 future price

Clearly this doesn't make any sense. If your earning yield for 200 days generating MATIC and it's future price is $500 per MATIC, the yield wouldn't be only $187.53
Hope that makes sense?
The calculator assumes a linear-return as the number of days progress towards the calculated Future Price. In reality, as that price is reached, the underlying fees generated have increased in value.
Take note here:
1 day position = $0.94 return
200 day position = $187.53 ($0.94 * 200)
In reality, the position would be generating MATIC and USDC, where MATIC is increasing in value. So a linear return isn't the ideal calculation here.
When the position of days is increased, I would expect to see the return of MATIC and USDC increase rather than stay the same - that way it could factor in increase in value.
Simpler way to view this problem
It's easier to visualise if you increase the Future price to be something extreme like $500 in future, across a 200 day position:
Take note of 1 day position, $0.94 yield, $1.5 future price
Take note of 200 day position, ONLY $187.53 yield, yet $500 future price
Clearly this doesn't make any sense. If your earning yield for 200 days generating MATIC and it's future price is $500 per MATIC, the yield wouldn't be only $187.53
Hope that makes sense?