There seems to be no way to force the size of the jump engine in the Ship Optimizer to be larger than the minimum needed to jump the ship. This presents a bit of a problem, as I often design jumpships with a little headroom so as to be able to act as jump tenders for later, larger designs.
And, if I have used the Design Propulsion function on a design, I am then no longer able to modify the engine-related components manually, so I end up having to manually set up a new design with all the components of the old, and then add a jump drive.
EDIT: Also, when you manually build up a ship in the planner, it displays speed in the stat block, but not the range.