Small tubes, "small" sound?

[GainFreak]

Hi,

Some people claim that the subminiature tubes like 6021, 6112, 5902 etc. sound "small" because of their overall small construction. The bigger the tubes they say the "bigger" and the fuller sound they produce unlike the subminiatures which at best sound like a good transistor.
I wanted to ask those who are more into the matter whether these assumptions are based on any hard theory and/or facts or it's just an assumption based on poor experience with those tubes?

[daz]

I think it's psychological. I used to think that about EL84 vs 34 or 6l6. Then i thought about it and realized it's just not the case, but that was picturing thier sizes and thinking along those lines. I've gotten some huge sounds from EL84's that were as big as any bigger bottle. It's more the circuit than the tube IMO.