Current behavior:

The picture is taken from the Blackwing Warlocks in Blackwing Lair. Their shadowbolt cannot be interrupted, so the Uninterruptible border shield is displayed on their cast.
I have increased the size of the spell icon on my targets castbar, and now it doesnt fit inside the shield.

This issue is not specific to this monster or this particular spell. It applies to all uninterruptible casts with my setting for increased spell size icon. The screenshot is just an example of what it looks like

Intended behavior:
When the spell icon on target castbar is increased, the border shield should grow to match the new size setting