Ok so I'm on Mid's and looking at Energy Aura and slotting Overload with it's 1000 sec recharge.I put 3 lvl 50 recharge IO's and then it's 502 sec.I put a fourth one in and that makes it 486.Five puts it at 472.Six put it at

458.I thought diminishing returns made more than 3 moot.Is this an error with Mid's and if so can someone explain how to calculate what the numbers would actually be.Thanks

As to the "more than three is moot", no this isn't an error in Mids. While they don't provide zero benefit, they provide a small enough benefit as to render them moot. Your 1st three enhancers netted you a total of 498 seconds of recharge reduction. The final three netted a total of 44 seconds.

As far as calculating the Diminishing Returns due to ED, check out

this page from the wiki. Of pertinence is the first sentence under each schedule type of enhancement - there it will list the benefit of each like enhancement added to a power (note: the values listed are for SO's). So in the case of your example, you're adding Recharge Reductions, which is a Schedule A enhancement type. The 1st two each provide a 33.33% bonus, and then Diminishing Returns start to kick in. The third provides a 28.33% bonus, and the fourth, fifth, and sixth each provide a 4.99% bonus (again, those numbers are for SO's - IO's values will be slightly different).