The idea behind Va isn't so much to do with max elevator deflection as with the capability to withstand vertical (upward moving) gusts.
The idea is that if flying at or below Va, the wing stalls, thus disposing of the load, before reaching the standard +3.8g (or whatever) design limit.
The stall speed, Vs, varies with aircraft weight. An aircraft loaded to MTOW might stall at 60kt; the same one loaded say 20% below MTOW might stall at 70kt (I don't recall the formula).
Therefore, the same aircraft, if lighter loaded, will need to fly slower (i.e. closer to its actual Vs) to be at Va.