There is no definitive figure for it. Your weakness is most likely based on your body's unfamiliarity with the movement although you should take your leverages into account as well.
The more hip dominance you had in your PL squat the bigger the difference and the harder the transfer will be. So if your low bar was wide with your ass 3 miles backwards I'd say the relative % would be pretty damn high. So less hip dominance in low bar = lower relative percentage.
Me for example, I'm a hip dominant squatter, but my low bar isn't like Louie Simmons wide and hip dominant, my stance is just outside shoulder width and I go pretty low, so I would imagine I could get my high bar pretty close to my low bar if I focused on it.
The only way to find out is to squat only Oly and see how far you can get.