I well known cattle breeder that wrote a book on linebreeding said if the percentage of one parent is 50% or less it’s linebreeding. He hates inbreeding father, daughter, mother son etc. for 140 years has maintained a line bred off one bull. Through rigid selection. He hates inbreeding and that one bull maintains a relationship of a grandfather through his herd. I would inbreed off a spectacular individual to try to solidify and magnify the trait. Immediately I would cross to a related family. I prob digress. He would say that was solid linebreeding because the percentage is less than 50%