That is a fast drop! There are heat sources made for animals that might be safer than a lamp. And some draw so little power you can run them off batteries (thinking it could be brutal if you supplied heat, then lost power.) Good luck!
Is the heat lamp over the straw? How old are the birds? They might not need supplemental heat. If you insist on a heat lamp, I’d have it secured in multiple spots so it can’t possibly fall onto the straw.