In an interview with the current Engineer of the Masterpiece line (Graciously translated by SydneyY over at TFW2005), Shogo Hasui states that (Moving forward) the MP line of figures will all be in scale with each other as a further focusing of the MP line; Now whether he was referring to the Alt or Bot mode I'm not sure, but given the past 2 instances (MP9 & MP10) I'd say he's leaning towards Bot mode myself.

Oh, and I don't see that silhouette as being Soundwave - Looks more like Hound to me.