I bought a Voopoo Drag X plus and the issue of no boost is a real problem for 'high' resistance vapers. If i use a 1.2 ohm coil the mod maxes out at around 12 watts. 12 watts (i had to repeat that because it is close to unbelievable)... Advertising the device as a 100w output is misleading at best and, in my opinion, an outright lie.
I suspect the same issue is happening to the OP - He's hitting the maximum un-boosted output of the mod.
Still, it's a valuable lesson - if there is no voltage output listed in the specs chances are that the device has no boost and is next to useless for anyone who vapes high resistance tanks. Looks nice though.