Rope length?

I just added 5ft to my rope length and I noticed that I was a lot slower back there, and there seems to be more drag. I was not responding well on my toeside jumps; I couldnt get up to a decent speed until about 15-20ft from the wake, which was really slowing me down. I bumped the speed from 22mph to 23mph to fix them problem. Is this normal? I thought that was a big boost in speed for only 5ft of rope. Does that mean I will have to bump up 1mph for every 5ft of rope?