I am Spartacus said:
I'm glad you could suss out the issue.....
Never go lower down the 'food chain' than tiagra...
You're always gonna get stick from Sora users for that one.
My 8 speed Soras have operated flawlessly for 6000 plus miles when i sold the bike, probably still going now.
Mind, it may be the price difference between Tiagra and Sora may make the upgrade well worthwhile..(ive no idea what the price difference is in general)
I think in general it will be an issue with the individual shifter, not the range. I had a Campag Xenon setup that buzzed like crazy. The same solution mentioned above was used. My newer setup with Xenon has always been fine.