Hello

In esp32_out.ld we have:
/* RTC slow memory (data accessible). Persists over deep sleep.

Start of RTC slow memory is reserved for ULP co-processor code + data, if enabled.
*/
rtc_slow_seg(RW) : org = 0x50000000 + 512,
len = 0x1000 - 512

The 512 comes from desired reserve amount.
Now ...