Your pepper plants really look happy! I like those pots you're using, too. Looks like they're 15cm tall and about the correct l/w to fit 3x6 in a standard 1020 flat. Seems like they'd be a good-sized container to use for growing sprouts up to plant-out size, with some extra depth for roots but also not too big as far as soil and space required.
Good luck this season!