This question came up in one of my classes and no one could really answer it.
In the equal field system in Tang/Song China the land was split upon the owner's death among others, that part was clear to us. What we couldn't find though it did the (wealthy) land owner's family inheritor have any say in what land he received during this change, or was in government decided? Surely some land must be more arable then others from all of which that they own, as some would be more preferred to keep than others.
You are absolutely correct that particularly powerful and wealthy landowners had quite a bit of say in how inheritance proceeded. But with that said, this is also because the equal field system didn't really apply to them.
The equal field system was primarily a way for the government to more effectively extract taxes from the poor peasants that constituted the bulk of chinese population. However, the government was limited in what land they could issue as equal field, primarily because of the existing ownership of the more productive land from wealthier landowners, who obviously were exempt from the equal field system (for example, most of the land around the capital was large aristocratic estates, not equal field). Because once again, the system was for peasants, not the wealthy landowners.
This is why equal field was mostly reimplemented in the areas of the north which the previous northern dynasties controlled. It seems that the system was never implemented in the south, along the Yangzi regions, as records show that the Tang government derived the bulk of its income in the southern regions from its salt monopoly and business taxes, as opposed to peasant farm taxes.
As well, there was no effective prohibition from the buying and selling of state land, thus reducing equal field effectiveness even further as what should've been peasant land ended up being consolidated further into wealthy hands in times where peasants were faced with dire hardships. Despite its detriment to state coffers, it wasn't uncommon for peasants to prefer tenancy under an aristocratic landlord to direct subjection under the imperial bureaucracy, for reasons quite analogous to the situation in the late Roman Empire. The wealthy could provide a degree of protection from imperial tax collectors, in exchange for the peasants' autonomy.
tl;dr - The reimplementation of the equal field system in Tang China had to co-exist with existing private ownership (which was likely larger, and owned the most productive land), so was thus relegated to second tier land. Thus any theoretical egalitarian inheritance of equal field was disrupted by wealthy private interests.