Having edited .profile to include
export MNTTOOL="1024 50"
and lived with my preferred placement for a few days everything is fine except for a single, cosmetic issue.
With mnttool running, connecting a USB flash drive and refreshing mnttool results in the drive being correctly included in the mnttool list, however the entire mttool window moves down the screen. Both the top edge and bottom edge of the window move vertically down the screen. Attaching a further drive repeats the process.
Removing a drive and refreshing mnttool, the top edge of the window remains in the same (lower) vertical location and the bottom edge moves upward to account for the removed drive.