Ice burst Defensive casting does not give correct xp

What I did: Ice bursted some mummies with my fancy new ancient staff on defensive casting (Was not possible until the ability to autocast was implemented)

What I expected to happen: receive 1 xp per damage done (5xp on 5x)

What actually happened: Hit a 20 and only received 50 xp on 5x (10 xp for 1x, or .5 xp instead of 1xp, Half)

IDs of related NPCs/items:

2009-era source (if relevant):

Screenshots or video: 2023-06-02_13-00-26.mkv

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I thought it was 1xp per damage, wiki from 2009 says 2xp per damage, but Im not too sure about that. Worth a look though.