PVT PLT OF A C172 FAILED TO FOLLOW THE TRACK DISTANCE FROM THE RWY ON A VFR DEP PROC THAT THE TWR CTLR BELIEVED TO BE THE CORRECT DISTANCE.

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I WAS DEPARTING BOEING FIELD FOR A DEST SE WITH WINDS FROM THE N. THERE IS A DEP PROC; 'VALLEY DEP;' WHICH ALLOWS PLTS TO 'SQUIRT' THROUGH SEATAC CLASS B AND RNT CLASS D WITHOUT GOING INTO THOSE AREAS. IT'S MORE COMMON ON TKOFS TO THE S BECAUSE ONE MAINTAINS RWY HEADING; THEN FOLLOWS RAILROAD TRACKS OUT. WHEN WINDS ARE FROM THE N; PLTS STAY TO THE SIDE OF THE TRACKS; DEPENDING UPON THE RWY. I DEPARTED RWY 31R THEN WAS ADVISED TO MAINTAIN A 'CLOSE R DOWNWIND.' I'VE ALWAYS INTERPRETED THIS AS 1/2 MI OR LESS FROM THE RWY AT PATTERN ALT (1000 FT FOR SHORT RWY 31R; 800 FT FOR THE LONGER RWY 31L); BUT THE CTLR ADVISED OTHERWISE. HER USE OF THE TERMINOLOGY MEANT 1-2 MI; AND SHE WAS COMPLAINING WHEN I'D FOLLOW THE ORIGINAL LESS THAN OR EQUAL TO 1/2 MI ABEAM. I'D SUGGEST THAT WE USE SPECIFIC DISTANCES TO AVOID AMBIGUITY; ESPECIALLY IN CASES WHERE IT APPEARS THERE'S DISAGREEMENT. CAUSAL FACTORS: I USUALLY USE RWY 31L OR RWY 13R; THE VALLEY DEP IS NOT WIDELY USED SINCE IT INVOLVES MANEUVERING THROUGH A LOT OF WEIRD AIRSPACE. I HAD DONE THE DEP ONLY ONCE BEFORE; THE DAY EARLIER WITH AN INSTRUCTOR.