Ticket Element masking for Fee totals

Hello!  

I'm having a real struggle with this at the moment, so was wondering if anyone can help?

We are applying an optional fee at the Performance Seat level, and rather than just having the £2.00 price on the ticket, we'd like it to actually have a clearer explanation.

I'm using the Ticket Design Data Element 'Total Per-Seat fees', and the mask of: 

Case(val When '2.00' Then '(+ £2.00 fee applied)' Else ' ')

is there something glaringly obvious that I'm missing here? (I'm guessing so!) as all I can get back from it is the ' ' (the else clause).

Without the case statement, it happily returns the 2.00 value (where relevant).

"Help me Tessitura Network, you're my only hope...."

Thanks,

Paul.