Is this right?

Ok...you are testing my memory!!! IIRC, the disc SHOULD measure .310 thick maximum.

The thicker the disc, the lower the fingers will be.

What you can do (it's done all the time but many people are afraid of it...it works) to get the finger height up is either do as I mentioned above, OR, you can get some parallel ground flat washers about .060 thick and put a washer between the flywheel and pressure plate at each bolt. This will effectively raise the fingers. Again, going from memory, a .060 washer/shim will gain you almost .100 in finger height.

As the disc wears, there will come a time when the fingers are too high. Then you pull the washer/shims out and go some more.

Just make sure the bolts holding the pressure plate to the flywheel still have enough thread engagement with the washers under them.