While no one would have any issue with them on 32mm, they are currently on 25mm with very little evidence of this changing. Currently 99% of Eldar, Dark Eldar and Harlequin Infantry are on 25mm.
The only exceptions I can think of are the much bigger Grotesques and Wraith Guard, or some Characters.
Yes, the Ranger from Blackstone Fortress is on a 32mm, but she is a Character.
Even if
GW released plastic Rangers (please!) on 32mm (hope not), you would still be perfectly within the legal rules to take them on 25mms.
The only valid reason to base them on 32mm is to make some cool basing like bushes, etc for them to hide behind
I disagree. Single wound T3 like Aeldari and regular human models are more "proper" on 25s, even if they "look" good on 32s. 32mms should be reserved for Characters or models with T4+ and/or multiple wounds.
This is, of course, just my opinion, but is seems to align with many basing decisions
GW has made (with some exceptions, like Pink Horrors and Bloodletters)
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