Konis have the reverse problem of being too long - had to grind down the little pad on the bottom of the insert to fit.
Either way the most important thing is that the insert is tight in the housing. You will definitely need spacers if there is movement.
A washer under the bottom of the strut is probably the easiest and safest.
Check also that the gland nut is threading correctly - they are a very fine thread and pretty easy to cross thread if you don't be careful. If they are cross threaded you may get your torque reading before you are actually tight down on the insert.
And it would suck big time.
Pete