I'll put this as bluntly and succinctly as I can because I find the LIR distriction arbitrary...
I have an ipv6 direct assignment from ARIN.
I am assuming you are an enterprise in PI space and not an ISP in PA space?
It is sized to meet the needs of my enterprise consistent with needs for future growth number of pops, prevailing ARIN policy etc.
Because my network is discontiguous I must announce more specific routes than the assignment in order to reflect the topology I have both in IPV4 and in IPV6.
I fully expect (and have no evidence to the contrary) that my transit providers will accept the deaggreated prefixes and that their upstreams and peers will by-in-large do likewise.
If you are in PI space, I believe most people take down to a /48 as a /48 is generally accepted to be a single "site". So let's say you were given a /40 and have several disconnected sites. Most people are going to accept a /48 from you in PI space. I would say pretty close to "everyone" is going to accept a /48 from PI space. An ISP that has been given a /32 or larger allocation from PA space and might have 10,000 customers each assigned their own /48 could instantly more than double the size of the IPv6 routing table if they disaggregated that /32. The problem here is that each /32 is 65536 /48 networks. An even larger net, say a /30 that disaggregates due to a router configuration goof means a potential of a huge number of networks suddenly flooding the Internet.