I’m hanging a double radiator onto a dot & dab wall & will be using corefix fixings for the brackets. I’ve drilled one side where there was a hollow spot on the dot & dab & so I could see where the board ended & masonry began, it was about 45-50mm of a gap. The other side I’m drilling right into the dabs & felt like I still wasn’t getting to the masonry but I’ve drilled about 100mm now & don’t want to go any further, what should I do?