Irish, Not half-way down the Fell but almost all the way to the bottom of the Fell.

I measure Jackets to between 1/2" & 1" above the bottom of the Fell.

As you are measuring also take a look at the sleeve length. The Hem of the Jacket should be almost the same or 1"-2" above the bottom of the sleeve.

These numbers are just rough estimates to give you the general idea.
The only way to know for sure is to have the Jacket and Kilt on and make a chalk mark on the Jacket at the bottom of the Fell of the Kilt.
(someone else will have to do this for you of course.)