Like, ~4 bits? It's the last two digits in 2a01:cb14:cce:1200::xx.

Compare these two:

  2a01:cb14:cce:1200::xx
  203.0.113.42+192.168.1.xxx

Which is shorter? It's not the pair of v4 addresses.

where does this comparison come from ? currently I only have to know 192.168.1.xxx

If I were not to use a DNS, I would have to know by heart my IPv4 address (32 bits) to SSH on the router, then hop on the right host (32 bits local address). I guess you could shorten that to 32+8 if you were to use a super common prefix, but I tend not to do that to facilitate routing when bridging networks with a VPN, so it is more like +32 or +24 (10.x.x.x instead of 192.168.x.x).

The full address I wrote above is 72 to 80 bits, depending on how you count (if the ::11 counts as 8 or 16). So that's more, but not much. And The common part is always 32 bit more than the common ipv4 part.

An easier alternative to hoping on the router would be to assign a port to each computer behind the NAT. That makes 32bit for the IPv4, and 16 for the port. Contrast 64+16 in my IPv6 case (I actually have a /56, but that's no help for remembering it). 1 computer on the network means that you have to know 66% more bits with IPv6. Bump that to 10, and it's just 16%. This is because there is always a common part, and that common part is two times the length with IPv6, so that makes it a constant offset.

When configuring a network, I typically do not know the prefix by heart, so I make sure to have that written on a paper sheet that I take with me.

Plot twist: I do not know my IPv4 by heart. I actually know the IPv6 one better, as I have a dynamic IPv4 at home. And I intensively use DNS/mdns. IPv6 actually makes it easier to use DNS for local network machines, I think, as I feel it is more worth it to fill the DNS entries with it, in case I want to later open some ports in the firewall for the www to access.

It's the full addressing of the host... but you're right, I guess it was a bit of a non-sequitor. The only parts you have to actually know are the xx/xxx, which is roughly the same amount of bits. They could even both be, say, "42", so you're remembering the same thing for both.