This plot is from the SN74LVC1G123 datasheet. You can see that the "K" value decreases as the supply increases, but it also is dependent upon the timing capacitor value. Changes in the K value directly translates into a change in the output pulse width (tw). The equation for pulse width is:
tw = K * R * C
Varying K will directly vary tw by the same amount, so the above plot can be used directly to determine the change across a certain voltage supply range.
The application report Designing with the SN74LVC1G123 Monostable Multivibrator has some useful information regarding designing with these devices.