After reading this post on the NA forums the whole thing makes slightly more sense why there is a rank to surplus as well. In beta 3 I was able to reach rank 30 MAR w/o a problem. Kuro and Soap had exped with me a decent amount and we had noticed I would always gain quiet a bit more Skill then them when we all had surplus. I was normally 2-3 levels above them as well. One difference that I had early on to them was surplus rank. It started at 1 and rose to rank 15 on the first day on Phase 3, while my MAR rank was 17. They at this time had reached rank 15 CLASS with a surplus rank I believe highest i heard from Kuro was 8 at the end of day 1. I had started leveling before they logged on I believe and reached surplus to the point of only gaining 10% rank exp, while they had gained quiet a bit more. The next day the servers were shut down and we we're able to log on the day after our surplus had turned back yellow but their surplus was hitting them harder then me even though I had gained far more rank EXP then them.
The next week after this possible reset on Tues. I was able to level 2 days straight w/o having any surplus, and finally hit it again when I reached level 1/4 of the way into 24. Then I continued to exp through surplus reaching rank 20 surplus. I stopped for a day to work on smithing and was able to get that to 13 where I hit surplus for that, and grinded through that till rank 3 surplus. The next day my surplus had went away again to white after about 18 hours of being away from MAR. I hit the surplus threshold quickly again, but it did not seem to reach cap again at this point no matter how much I exped. I grinded constantly till 27 at this point and then decided to switch back to smithing rank 15 with rank 3 surplus. After a day away from smithing surplus was just as bad as the day before. The next day I returned to MAR where I started at white till 28 where I hit a 10% skill gain because of surplus. Returning to smithing it was white now, but I quickly returned to yellow with surplus.
I decided to grind at this point to close to 29 as I could. I hit surplus of 50% where I was having a hard time finding mobs that would give decent rank at this point so I was barely able to reach 29 with 1k rank into it. The next day leves/exp reset and ended up grinding through mine and others leves to 30 where I never reached surplus till about 2/3 way through 29, and it stayed at 10% of my rank exp at that point till 30.
The exp from phys always was declining never increased just how they said, so not gonna bother talking much about that. Did not seem to decrease as fast as rank though.
This leads me to believe that the surplus rank either increase the exp/time between each threshold or increase the rate of recovering from surplus. If this is true the best thing to do is grind like crazy to get your surplus rank high. I'm gonna test it in OB to makes sure, but through my experiences I'm fairly confident surplus acts as you body wearing down. However, the more you wear your body down, the faster it can recover and more endurance you have. So there seems to be a definite way around it.