The tables in the link below may help with some starting points. If you want to start with minimum contrast use max yellow, no magenta. Or use an Ilford #00 filter.
Note however the "split grade" approach is just a specific case of the general technique of using multiple filters. It does not bypass the potential need for local controls such as burning and dodging in the print. And when you use a short scale, high contrast film like ATP you will likely need some burning and dodging to help bring out whatever detail there is in the negative. Start at the lowest contrast and go from there.