My wife has a full head of hear too (unlike me!) and is very happy with the deflector's reduction of buffeting at speed...
I know exactly what you mean - before drilling the holes as shown on the Chrom Design instruction video (the one with the guy who has a questionable taste in wrist jewellery) I placed some masking tape over the site to be drilled, and marked it accordingly with a fine tipped pen after offering up the deflector and pushing the location bolts hard against the tape. The area behind the seats of my Spider is carpeted (though in the video it is vinyl) and this left a good impression which made marking easy. Once the deflector was removed, check the markings are clearly visible and locate the centre of each. Drill the first hole using a 4mm drill and work up thro' 8mm, 10mm until you finish up with a 12mm - it is surprising how much pressure it takes to cut through!
Once you have completed drilling the first hole, offer up the deflector again and double check the location of the second hole. This took quite a while, but once you are happy then repeat the above.
To avoid pulling threads out of the carpet, I used a braddle to make the initial drill into the carpet and ensured that nothing was pulling from it, after that go ahead with the 4mm.
The location bolts seem a little short but maybe they were designed for the vinyl backed area as previously mentioned. However, they do just fit and I secured the plastic nuts with a spot of glue to ensure they don't vibrate off over time.
May I wish you all the best if you go ahead - it does make a difference when fitted (particularly, it seems, for the ladies) and I found it cuts out all the buffeting around the shoulders when the windows are up...
All the best!