On non-dry runways, risk of runway excursion during an RTO becomes much more significant, even when commenced at V1. By selecting a lower V1 from the range of available V1 speeds, you can mitigate this risk, but it also means you are potentially taking any issues into the air, even though you probably have margin to stop at speeds above the selected (low) V1. This could be potentially useful if you are taking off from a tabletop runway, where any runway excursion would be catastrophic.
On the other hand, you could select the highest V1 possible and your calculations would be stop-minded, which means you are willing to risk a potential runway excursion, because taking an aircraft into the air with performance issues could be potentially worse (e.g. Innsbruck, Salzburg and other similar airports with close-in very high terrain).
It's up to the operator to decide which option they prefer, and this can vary from one airport or runway to another. I'd suggest contacting your performance pilot/department, and they should have more information on what they use for your calculations.