Anything below is under the condition that you have found the sweet ratio of gpu/memory clock and got the thread concurrency, voltage, etc right.
Setting intensity 20 will very likely result in lower valid shares, thus less pay.
You all probably already know the reason: the pool is calculating your Kh/s based on your VALID shares submitted.
And the lower Kh/s on pool is resulted from the invalid shares submitted. And the invalid shares are from a few sources. But there is only one them of you can actually improve by yourself.
Although you may see a higher Kh/s on cgminer by setting -I 20, your cards are working very very hard and sometimes results in bad calculations and therefore contributes a large portion of to your invalid shares.
Setting it to 19 will improves your valid shares and thus higher Kh/s on your pool at least by 3%, even though you are seeing a slightly lower Kh/s on cgminer.
For example, I have 4x 290x all are at -I 20 and getting 883Kh/s each based on cgminer(totaling 3530Kh/s), that is the actual speed of my cards are working at. However if I go to my pools, I will find different Kh/s sometimes higher (4000+) than cgminer and sometimes lower(3000), but mostly lower, because of the invalid shares are eating my cgminer Kh/s.
After setting to -I 19, my cgminer shows 871Kh/s reach so totaling 3484Kh/s (-I 18 will get me to 830Kh/s, which is too much lower), but now the pool is reporting even higher Kh/s than my cgminers(about 3600Kh/s) and 0% invalid shares almost every round.
Why higher Kh/s than cgminer? Because a lot of other people are using -I 20 because it looks nicer in cgminer, however getting invalid shares, and the pool is thinking YOU are using better cards because it only counts your valid share to calculate Kh/s.
Try it out yourself.
If you find this helps, you are more than welcome to tip
BTC: 15DARf9fpp8Hn7MvUW33StP3knsZgsa398
LTC: LYcc9VKguWKfrsP2T7y1S3BeL1c1MFbF2s
DOge: D66DinpDEE8mZuBYgBadC7By1yXeX656TZ
Coinye: 5ogyMLgRQmCWHq897o1btPXp2ibd7tGJYj
42: 4H3k5Msh31dJ9nEbKAeuYibQdaLS1JzVK5
