But not six times. I mean, I have a 6x9 Fuji, and the images it makes are about 4 times as large as 35mm. And in any case, Holga/Diana cameras don't come anywhere close to that.

Well, going exactly from the quote, using surface area:

6x9 fuji: 54cm^2

35mm frame: 8.4cm^2

That fits roughly 6x

Holgas shoot 6x4.5 though, half that, and Dianas are 4x4, even less. And 35mm is really 24x36, closer to 8.6cm^2.

Holgas shoot 6x6 or 6x4.5.