The animated shorts in the end of Neo Getter Robo Versus Shin Getter Robo had them all pretty much the same size, save for Gloizer X ( SP?) and Shin Getter Robo, which was a bit bigger I think. I've not seen this electronic Manga though...
Hmm, looking at the size maximums, I think robots like Daitarn 3 and Gunbuster are out out of the question.