Standard fingering Fdim

I know it's whatever works along with where you're coming from and going to, but... Index on the G and middle on the E, or the other way around?

Going from C to Fdim to C again.

"When I Fall in Love"

yep, index on G, middle on E, ring finger on C, pinky on A

to go to C chord just slide the pinky up one fret, then back down again for the Fdim

You could also go up to 4 5 4 5, using the same exact diminished finger pattern at the 4th fret instead of the 1st. Its the same chord, same notes, just in a different order. Just like Eugene said, but slide your pinky up to the 5th fret. Its always nice to have options!

Thanks for the confirmation. I've always played that shape the other way and its a tough change for me.

Starting to get used to it and it makes the progression so much easier even though it felt wrong at first.

But the other is appropriate and traditional too depending on the transition, right?

It always depends on the transition.

For example, when I play Uncle Rod's Uke Boot Camp in C, there's a CM followed by a Cdim. In that case, I'll play the c'' with my pinky because that makes for an easier transition to the next chord.

But in A where we have AM followed by the same Adim (same as Cdim why that's true is an exercise for the reader), I use the "standard" fingering for both.