I would fill the pot`s, your only use half the space and the smallest part of the pot actually
root`s are so important, with out a hugh healthy root net you wont grow anything near a 4oz plant, and weed have as much roots as it have grow above the soil, or said in another way, the size of the root net decide the size/limit of your plant, when you do your next repot make sure to fill em up, don't barrie more then a inch of the steam, old top soil layer must also be close the be the new top soil layer, and use a good amount of perlite or coco in the mix for draining, clay pellets can also be used, weed like airy and light soil for oxygen, don't like to stand in wet compact soil all the time
if you want a 4oz plant out of them, you need, like most already said, a long veg time, and with a longer veg time you need a bigger pot, much bigger (I use 5 or 7 gallon as my final pot`s depending on how much veg time/size and I usually veg em to maturity = atleast 5-6 week`s and that is plus the 2-3 week`s as seedling =7-9 week`s from seed, that give me 2-3 oz plants but its also indica`s that finish in 7-8 week`s a Sativa plant that flower for 12-14 week`s can easily yield them 4oz if you do your part)
Ooh yea, and when you water, water so all the medium get wet/moist and you see some run off, then wait until pots feel light to lift agin until your next watering