@Michael Duncumb
Question is are you using original foam and and how much push back does it have. I see you're recovering using seats to sell to show you're craftmanship and quality. With that said judge the foam on age and use. Not sure how you pattern for new covers tho. Do you mark the old covers before removal and cut them up to pattern for NEW covers?? If so and using original foam I'd suck them in a little on seam allowance then steam foam after the covers are made. Again that depends on used foam quality and use. Or add sew foam 1/4, 3/8, 1/2 to covers and/or original foam to fill out covers. Again its all about how much you want to spend and sit one to shop your craftmanship.

As to the V cuts in seam allowance you almost always have to do it with Piping/Welt because of the 4 layers and certain radius.(this also depends on your seam allowance you use). Be careful tho, cut too big of V and too many with a tight cover they will show. Sometimes you just cut slits(reliefs) and trim you're seam allowance back. If you get good enough sewing you let the machine do the work and they will lay flat. Practice helps, just play with different ways

Where did you purchase the mini seats. Just started on my own.

Are you using a welt cord foot (pipping)? I find things are flatter around corners. The feet are cheap on E-Bay.

Did you pre make the piping with glue?

Apologies for the delay, I've recently moved into my own unit after working in a garage for too long!

@Justin L Rash I've used the original foam from the seat, when I took it apart it appeared to be in good condition. I also used 6mm scrim on the front and sides to give the seat more cushioning and pad it out. I had some patterning vinyl I used to make the new panels and did reduce the edges by 1/2cm on both sides, not sure if this was my issue. I did also cut the seam allowance down but didn't add V cuts, think that was the nail in the coffin for these. I did steam it out which helped a bit but I've learnt a lot now they're finished.

@Manny Bencomo I picked them up on Facebook marketplace, I'm in the UK so there's always a Mini interior for sale somewhere.

@Wayne Munro yes I am, 1/4" piping foot and 3mm hard plastic piping.

@Gareth Judd I've never glued piping for the same reason I've never glued material to scrim. Namely that it restricts the movement when you go to fit the cover. I typically sew the piping before attaching it. Is there ever a reason to glue it or is it a big no no?

I am new to seats, the last trim shop I worked at I mainly did everything but seats. I've done a lot of seat repairs in the past so I like to think I'm fairly proficient but I know there is a huge mountain yet for me to climb!!

Thank you for all the responses! I have finished them, there are still flaws but overall I am happy with the way they turned out.

Are you cutting your welt strips across or up the roll? It appears you are stretching it as you sew.

I agree with Justin, the cover isnt tight enough to crush the foam in the seam. And alway flip the seam so it lays flat.