First install on my own many many years ago I watched in disbelief as the run went across the penultimate tread and up onto and then across the top landing, I had never seen a carpet fitted which hadn’t had the carpet cut across the bottom of the top riser. I’ve since seen a few, but thankfully no more runs of that length.
I find if the carpet is a twisted loop then just going very slowly with the screws does the job.
Worst thing I’ve seen with carpet was a white shag pile at least 2″ deep being fitted to stairs, it was flat within a month. I had to move an old AC Stratus for them to fit it and the carpet fitter gave me a hand to carry the rail back in, stumbled and put his grease covered hand right onto the carpet. His face was as white as the carpet and then turned a little bit green as I attacked the stain with WD before the homeowner walked out to spot it.
I shall bear that tip in mind cheers.