Anything better than J-channel for this?

I'm building a shed.

Intent is to trim it very much like this picture, to match the rest of my house (this is not my pic, though):



I'm using vinyl soffits and then either vinyl or aluminum fascia, plus I will try my hand at fashioning that corner piece out of aluminum. I have aluminum drip edges already installed.

My question is: Given that the soffits are only 1/2" thick, is a 5/8" J-Channel (all Lowes had) really the ideal? I would have to install the J-channel like this:



The shed is already sided in SmartSiding and I've found that if I attach the J-channel, the soffit just doesn't fit all that snugly. Perhaps this doesn't matter after all? I'd have to let the fascia set a bit lower also so that the soffit is still level after it "sinks" in the J-channel.

TIA. This is my first time ever fiddling with trim at all I could have done wood but this is way cheaper, way faster, and no maintenance!

 

Your two pictures show different soffit construction so what you have will help determine if F or J channel is best.

Depending on how your shed is built I usually do not use F or J on the outer edge. Instead the bottom lip of the fascia is what holds the soffit material in place, much like the picture on the right but without the F channel (even though it's labled J and points to both, it looks like J at the house side and F at the fascia). Not having the flange of the F on the fascia helps your trim material lay flatter.

 

Great point--the pic is mislabeled, and in fact this is what I had intended--that the lip of the fascia would hold the other side of the soffit as you describe.

Thanks! It sounds like this is the best approach then. It seems like the J-channel for aluminum may be a little tighter fit, so I'll see if vinyl snugs into it better but otherwise I'll do the bottom right pic and no f-channel, just one J and the fascia.