No, I don't really think size has anything to do with it. Unless, of course, you're comparing the exact same attack to itself. In which case a larger version is either 'less dense' or just has that much more energy in it. I know it's a game, but take the Legend of the Super Saiya-jin for the SNES as an example here. At the end, if you use a full powered Kamehameha, Spirit Bomb, SBC, Masenko, or Galic Gun they fill the screen because there's a lot more power behind them.
But to get down to the specifics of your examples I'll go over what I think on each case.
Take for example Piccolo's makankosappo, it's circumfrence is quite small. and would be about the thickness of his arm. But yet the effects of the attack is devastating, even being able to pierce through Raditz who is approximatly 3-4X stronger than Piccolo. If Piccolo had expanded the beam to make it as thick/wide as say a kamehameha, would it have been a weaker attack?
The SBC (sue me, it's faster to type) looks specifically designed to puncture. Hell, it
looks like a frigging drill. I would say, in this instance, smaller is better. If it were too large it wouldn't be able to achieve the desired effect. Either simply due to being too large or to the energy not being compacted/concentrated/focused enough to punch through the target.
And yeah, if he'd simply widened the beam without adding more energy, it would have had less effect, IMO. I see it a lot like weight displacement. A normal sized SBC is like sticking a cane into the snow. An overly wide SBC is like walking on the snow in snow shoes. Same ammount of power, greater area of contact, less force in any one place. Large attacks, like the Spirit Bomb Goku used against Freeza seem to rely more on simply overwhelming the opponent with massive ammounts of energy.
What about Kuririn's Kienzan? A little bigger in width than a plate, but about as thick as a deck of cards. When fighting Nappa, a kikoho (a very WIDE blast mind you) isn't even able to touch him. SO when Kuririn fires off his Kienzan, Nappa thinks nothing of it and almost dies because of his ignorance. Can we say "oh, well Kuririn is stronger than Tenshinhan"? No we can't Tenshinhan has proven to us many times he is arguably stronger than Tenshinhan. So why would Kuririn's blast have a more lethal effect on an opponent? This even goes with Freeza! An opponent way out of Kuririn's league.
The Tri-beam is a powerful 'hitting force'. It's like the Kamehameha, it's a brunt force impact type attack. The Destructo Disc is, like the SBC, a specialty attack. It's designed, specifically, to slice. My thought is that energy discs like that have the energy focused into a really narrow and thing 'blade' around the edge with lots of concentrated energy allowing them to slice through even things that are considerably stronger than the creator of the attack.
Where as the 'hitting force' attacks spread the energy out over a wider area thus doing less damage to a single location. The more focused the impact, the more energy is hitting a single point, and the more damage is done to that point. So a weaker focused attack could do more damage than a stronger unfocused one.
You might say "these are all older episodes/chapters, nothing like this happens in the newer stuff". Well lets take a look at Vegeta's final flash. A very powerful attack that is seemingly a little smaller than a kamehameha. That cut through Perfect Cell like butter. Cell was much stronger than Vegeta when he used it.
In this case it's sheer power. The Final Flash is definately a 'hitting force' kind of attack. But it was a HUGE Final Flash. Vegeta poured ungodly ammounts of energy into it and kept it pretty focused (he managed to avoid blowing up the Earth with it, despite Trunks' fears) which means that, even though it was big, it was also packing a pretty big punch. As with the Spirit Bomb this would be a case of trying to overwhelm the other with the sheer ammount of energy.
That's my thoughts on the matter. I put quite a bit of thought into this for my Fanfiction so I know how I want an attack to function and what kind of overall look and effect it should have.
See we're all friends here.
