Ted has pointed out more than once that using through-hole components (ie large capacitors with legs) has some significant downsides because of their ability to act as antennas for noise, so for that reason if no other we are encouraged to use surface-mount devices. Since R6 is in an 0805 package it makes sense to choose a capacitor of the same physical size to piggy-back on top of it.
I imagine there’s a point at which increasing capacitance has some negative impact also. I mean in the extreme hypothetical case your inter-galactic capacitor would just keep soaking up current without the voltage ever rising to the level needed to function as Vocm reference. But I’ve no idea how much starts to be too much – I just went with what most others have done and have a notion that it was also Ted’s recommendation, ie 47µF. JK suggested 220µF based on his experience, and I have no reason to doubt that it would also deliver a good result.