I just use a 50ml syringe to top it up with fluid.
Pretty stupid design in terms of access in my humble opinion. Might be better on lhd models with the booster on the other side of the engine bay.
Depending why you're topping the fluid up, if it's dropped through general brake pad wear it's recommended not to top it up as the fluid level dropping to it's minimum mark and triggering the brake level warning is an indication of the pads having worn down enough to need changing (if anyone runs them that low)
Not an issue if you keep an eye on your pads from time to time.
Sorry if mine didn't sound like a sensible reply.
I can only report on what I have witnessed. I do not have a scooby wi the tools, so, when I needed the deed done I called Andy. The fella is the top dog, a full time ford tech and ST meister(although he has gone over to the Ultimate Green side
What he don't know about ST's, you don't need to know. So when he uses this this technique, as he , no doubt does every day for a living; I thought that may be the way it's done......hey ho!