Sorry – I see now that this information was in your original email.  I am not an expert on UEB Technical, but it seems you should be using the symbols in section 3.6 of the Guidelines for Technical Materials…there is a visible space symbol used for an omission that has no print symbol (dots 346).  I do not believe the three dot 5s would be appropriate here.  I would also suggest you post this in the UEB Math forum for confirmation.

Cindi