Determine the weld size as if it were flush, then subtract the amount that the weld is underfilled (less than flush).

You don't say whether its a flare bevel or flare-v, but that doesn't really matter because the math is the same for both. For a flare-bevel, the effective weld size is 5/16R, so, divide the radius by 16 then multiply by 5. That will be your effective weld size or the throat, then subtract any underfill. The rest is just figuring the effective throat of various fillet welds to find out what you have. For example: .750R div by 16=.041x5=.205 or 3/16" . You can round up or down as needed, but I usually take it to the closest 1/16th. Now, this part is just based on my experience dealing with engineers, if there is anyone out there that knows for sure, please let me know, but, if the drawings show a fillet weld and size at a flare groove weld symble, their probably meaning the effective weld size (it could mean the effective weld size for that size fillet) but the best thing is to fill it out flush, unless indicated otherwise.