Mountain shifters have a different amount of cable pull on the FRONT der than road shifters.
So, if you still have the old shifters, that "might" be a contributing factor.

You may also have better luck with one of the "A" FDERS (Altus etc.) designed for a few less cogs. They aren't quite as narrow.
7 speed chain is wide compared to a 10 speed FDER and pretty much asking for chain rub.

IF I were attempting to do the same, I'd use an FD-C102.