Actually, MP Soundwave is scaled quite accurately as you can see here compared to Sunbow's official scale.
The orange lines represent Sideswipe's height. My MP Lambor is obviously leaning backwards in this photo so I've adjusted the orange line to where the top of his head would roughly be if he were standing upright (I can do a direct side by side comparison pic if you really want). But we can see that MP Lambor's height compared to Soundwave is roughly the same as the Sunbow scale.
Also compare Blaster's height. As Metallikato said, he is tall... but even taller than he estimated. Ironhide, Ratchet, Trailbreaker and Inferno's heads all come at around the green line, whereas you can see that Blaster's head nearly reaches the purple line, which is Optimus Prime and Megatron's height. And Soundwave is the same too - his head is just under that purple line. So if you want an MP Blaster with G1 cartoon scale, then making him around the same size as MP Soundwave (or possibly half a head height taller) would be accurate. Incidentally this would also make MP Broadcast about the same height as G1 Blaster! Yeah, that's how huge G1 Blaster is.Which isn't the fault of the toy which of course existed as a Microman figure long before Transformers came long, but there you have it.
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UPDATE
Here ya goAlso, the green line represents the height of characters like Ironhide, Trailbreaker, Grapple etc. The orange line isn't part of the original Sunbow bible's chart, I've added that in to represent the height of smaller Autobot Cars like Sideswipe, Prowl etc. See here for more.
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