justify/masonry style layout broken when thumbnail size is set above XS

[jjemil749]

Modus Theme stops applying the masonry style layout when thumbnail size is set above XS.
This has been confirmed as well by another user.

Discussion thread: https://piwigo.org/forum/viewtopic.php?id=29316

[dae1804]

This looks to be deliberate -- see line 2 in thumbnails.tpl: there's an explicit check to see if $derivative_params->max_height()<400. Changing 400 to (e.g.) 600 allows "small" size images to display. It looks like this limit was raised from 400 to 480 in a867f0d, then reverted to 400 in 2e67776 without comment.

What's the rationale for disallowing fluid mode for larger thumbnail sizes? The code seems to suggest concerns about not fitting at least one image per row -- is this a hack around a CSS issue? At minimum, can an option be added to make this threshold user-configurable?