I'm using the FWS mod together with alien biomes, and regrown trees have miniscule collision/interaction boxes. I'm not sure if this is a feature or bug, but it is certainly surprising. It'd be nice to be able to have them "normal" sized if possible, for sure.

Regrown trees should have the same collision/selection box as normal vanilla trees. Because they are normal vanilla trees. Growing trees' boxes should be scaled based on their growth stage.

Are you using SqueakThrough or anything else that modifies trees?

Ah, I am using SqueakThrough, yes. Guess that is what is causing it.

The collision box scales with the tree growth, but the tree sprite starts off as a fully grown tree, i think that is what is causing the confusion.

The sprite should be scaled down as well.

That doesn't seem to be working properly if that's an intended feature. Many of the trees in this screenshot are seedlings/saplings, and if you mouse over them you can see (Right hand side, highlighted tree) their hitboxes start off tiny and scale up over time, but the sprite pops in at full size and never changes. This is true regardless whether the tree was generated naturally, or from a hand-placed spore.

https://steamuserimages-a.akamaihd.net/ugc/781853033307649612/C80AAAFB529EF9709DEB88CD7E6036CA9F8295ED/

(Ignore the derpy setup I was experimenting with the charcoal/coal/fertile soil pipeline in creative :p)

I've observed this bug with no other mods running, these are my video settings in case any of these are messing with how sprites are processed/handled:
https://i.imgur.com/8iVS6Ua.jpg

I don't suppose you have a save, close in time (ideally exactly) from that screenshot?

Sadly I don't, I didn't bother save as I was just experimenting. However, I just created a new save that I think will help the same way.

Save file: https://www.dropbox.com/s/wiqec1f3e1o3qog/Feesh%20and%20Wildlife.zip?dl=0
Screenshot: https://i.imgur.com/HGP2jBH.jpg

The cluster of trees near the player are all freshly placed saplings that are displayed full size with tiny selection boxes when viewed on my machine (V0.17.x experimental, no other mods installed)

Ok, yeah. Derp. This is a problem that occurs because when FWS makes the growing tree entries (copied and adjusted from existing trees) it doesn't properly handle the definitions for the HR sprites.

I can confirm that this issue is a v0.16< issue only, after migrating our modpack to v0.17+ we finally had regular sized trees, matching their hitbox.

In 0.16 it will scale wood amount and the hitbox but not the actual sprite.