[Info-ingres] set unicode_substitution command

[Steve]

select dbmsinfo('charset')
\g
Executing . . .

┌────────────────────────────────────────────────────────────────┐
│col1                                                            │
├────────────────────────────────────────────────────────────────┤
│ISO88591                                                        │
└────────────────────────────────────────────────────────────────┘

set unicode_substitution 'X'
\g
Executing . . .

* select u&'\062E';
* \g
Executing . . .

┌──────┐
│col1  │
├──────┤
Wed Sep  4 16:40:17 2019 E_AD5016_NOUNIMAP_FOUND        Unicode code point 0000062E cannot be mapped to local character set.
││
└──────┘
(1 row)

Why am I getting error E_AD5016 here? I expected Ingres to return 'X', what am I missing?

u&'\062E' = Arabic letter Khah

Thanks
Steve