Multi sowing a module

OK, so your 3 seeds all germinate in a 2" sq module. I'm not sure whether a parsley and lettuce would cope being in such close proximity over time. I saw somewhere sowing 2-3 onion seed in the same module and planting out without separating could work but giving smaller bulbs. Would your resultant baby plants in the module be eventually stunted for lack of room? You know parsley and some lettuce are rather blousey and like to flounce. That reminds me I might get some onions sown today if it stays fine.