With all due respect, smiert spionom, that seems a funny explanation to me....
What's the source of your info?
Another urban legend?
I don't have any info about that,, but having a few thousand hours on the ATR I think the right power lever ( not thrust lever, it's not a jet, sadly...) is shorter simply because of the left condition lever, which needs room to move fore/aft.
Standing by to be corrected!
Regards
LEM