U+2A21 Z NOTATION SCHEMA PROJECTION should not be an alias of U+21BE UPWARDS HARPOON WITH BARB RIGHTWARDS. According to ISO/IEC 13568, page 24, “Schema projection ‘⨡’ and the mathematical toolkit character filter ‘↾’ are different Z characters”. In particular, U+2A21 is larger than U+21BE, similar to U+2A1F vs. U+2A3E or U+29F9 vs. U+005C.
By default, U+21BE is larger than U+2A21, which is the opposite of correct:

With 'NWID' enabled, they look identical:

- Your font version: Version 34.0.0
- Your font variant: Iosevka Slab Extended
- Your application using Iosevka: hb-view