IPv6 DHCPv6 Prefix Delegation

Hi REne and staff,
thanks for your work (it is not pretented)

i lab this lesson with

and i test some other prefix values for the global pool

When the global pool is /40 (like in the lesson) the delegation is between 40 and 56

when the global pool is /32 the delegation is between 32 and 48

it seems that the upper value is + 16
And you cannot use a value greater than the upper value (when /32 the upper value is /48 and you cannot use /56 for example)

Is there a reason for that ?
Regards