hi Shy,
you need an ejection speed higher than the blade speed.
IMO if you dilute the airflow on the trailing edge, you will loose efficiency, unles your compressor can provide enough air.
Having larger nozzles doesn't mean more thrust : just less speed higher pressure, but the same airflow (mass/seconds).
the thrust is made by the airmass/section/speed, so you won't have a different thrust. and the blade angular speed will be function of the thrust.
so, maybe locating the nozzle a little in the disk and making it longer may be the better solution (just an opinion).
BTW, the outer enveloppe of an airjet is what produces losses, if you increase it, you increase losses, the rounded shape is the better shape (less circumference) but , IMO, not the quietest.
the noise, from what i'vre read, comes from the airflow speed and vorticity. i also think there are some ways to improve that.
sorry if i am not very clear.