The Kentucky Derby Festival has raised the registration cap for its mini and full marathons in April, but officials say the spots are still filling quickly.Spokesman Mark Shallcross says 18,000 runners will be permitted in this year’s competitions, with most of them taking part in the mini-marathon. "We’ve gone to 15,000 the last three years, and we sold out basically mid to late March. Just to make sure we had the infrastructure in place, we increased the cap slowly," he said. Shallcross says the cap could soon be raised again because of the mini-marathon’s popularity. Again this year, runners in both races will begin from the same starting position indowntown Louisville.