It's a bit hit and miss …
Agreed that it’s hard to work out exactly what’s going on with layers and spells, but that something’s definitely squiffy.
I’ve never tried casting fireball on the duergar boat, for example, but I did try sleet storm and goodness knows where the slippery surface ended up but it certainly wasn’t on the deck of their boat as I intended. I couldn’t find it at all, despite the fact my druid was maintaining concentration on the spell.
