Why too short? You can stretch the spring in the endcap a few times, they are a replaceable item, and recommended to be changed at about one or two years time. Provape only charges about a buck for them, well worth it to grab a few.
Replacement ProVari 2.5 Spring
Also, check to see if your board is tight in the tube. Take a Q-tip just moistened with a little isopropyl alcohol an clean the center pin on the board. While doing this, apply a little pressure and side to side motion perpendicular to the circuit board and see if it "wiggles" a little bit. If it moves at all, the glue dots holding the board tight to the tube may have come loose, and the board may have shifted. This will require opening a ticket with Provape to have them re-glue the board into the tube...hope this helps.