how much do enhancements diminish - global recharge seems very low

This is in regards to a lvl 50 dark melee / fiery aura brute

I know there is some "enhancement diminishing" with multiple usages of similar enhances, but when i check my base recharge time bonus (under combat attributes) I see a 60% bonus... broken down as follows... five +5% bonuses, 3 +7.5% bonuses, and 2 6.25% bonuses.

Which is all good, but i have SIX +5 bonuses (the six includes two full Obliteration Sets). Do enhancement set bonuses only apply for 1st of any set installed - with no plus for installing a second copy of any particular set? That would explain the discrepancy of 5%.

But not why my alpha slot isn't boosting it. I have my alpha slot filled with a Spiritual Radial Boost - which should give my global a 33% increase - it says there is some enhancement diminishing effects - but shouldn't that increase my global recharge SOME above the 60%?

Well six will do you no good because of The Law of Fives You can only have up to 5 set bonuses of the same name work.

Also The Alpha slot won't boost your global recharge but the recharge in your powers.

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Thanks - that clears up a lot. I should be able to get it higher soon - looking into purple sets to replace a few of the +5s (already have 2 hecatomb - looking for other good sets to start accumulating)