Technically, it's a FMCSA requirement to go inside the rub rails if the load doesn't extend over them:

Proper Use of Tiedowns 

The new regulations require each tiedown to be attached and secured in a manner that prevents it from becoming loose, unfastening, opening or releasing while the vehicle is in transit. All tiedowns and other components of a cargo securement system used to secure loads on a trailer equipped with rub rails must be located inboard of the rub rails whenever practicable. Also, edge protection must be used whenever a tiedown would be subject to abrasion or cutting at the point where it touches an article of cargo. The edge protection must resist abrasion, cutting and crushing.

https://www.fmcsa.dot.gov/regulations/cargo-securement/cargo-securement-rules

Do officers actually enforce that? My guess is that they don't, as often as we all see how just about anything goes when using straps, except not having enough straps, having inadequate WLLs, or having cut/frayed straps.