Nano vs uno: max sketch size differences, why?

Why the max sketch size in a nano is 30720bytes and in uno is 32256 bytes????

It´s supposed to be the same microcontroller, ATmega328P, I don´t understand.

*** It´s possible to get max sketch size of 32256 bytes in a nano? How?

Thanks in advance!!

Nano and Uno have almost exactly the same schematic, but for some special reason, selecting Nano in the IDE reduce limits the ROM size by 1536 bytes.
This is because Nano has different bootloader size than Uno, in the past.
Both are the same now, but we're wasting ROM at the team's decision to keep things consistent.

Rewrite bootloader with miniCore.
Then use it as a miniCore forever.

It's down to different bootoaders, burn the UNO bootload to the NANO (First thing I always do when I buy one, after testing.)
This gives you the smaller bootload, so more space. If you have a programmer, you can use the Minicore linked above to give you ALL the flash space.

Ok thanks very much!, I tryed the optiboot bootloader and now I have 5% more program memory and fastboot. Great!