To which code are you welding? If you're going by D1.1, and your joint is prequalified, then the short answer is yes, you have to fill to the theoretical level of the base metal. NOW, since what you're describing is really a PJP flare groove weld, the 1/4 MAY be intended to describe a depth of penetration. The symbol you describe is incorrect, and the depth should not be called out as you described it. You should go see the EOR before you do anything.