furthur data
a customer's bike came thru shop today for a flat

it also had biopace triple, with a deore top shifter lever in friction mode
it had identical behavior
1-2 takes up more cable pull than 2-3

yes, cable clamp is correct and derailer adjustment is good
shifting works consistently, once shifted the rear cogs are all workable withou need to trim FD in any sprockets
seemingly indicating good responsive FD adjustment

I'am merely puzzled by the skewed cable pull and misaligned indicator mark for 2nd sprocket

more clues-
on the gripshifter I have, indicator marks are evenly spaced, same as with the observed deore top shift lever at work
however, on a different gripshifter i have laying around , the indicator marks have top biased spacing (seemingly correlating with the non linear cable pull Im getting)

suspect compatibility issue between different era components and subtle changes to FD swingarm design over time
undocumented?

ultimately a curiosity than a real problem, I can always remove the painted on indicator marks