This is one I got badly wrong over the board. I played 20/10(2).
This gives Red a ten-pip lead in the race but leaves White fifteen hitting numbers to at least equalise the position. Red should not be racing; it is too early. Even 20/15(2), 8/3(2) is the wrong idea. Red must keep the anchor for the time bring. Red should be looking at blitzing or priming White’s rear checker.
There are two moves that play to this plan. 13/3, 8/3, 6/1* which combines priming with blitzing and 13/3, 8/3(2), the pure priming play.
It turns out that these two plays have virtually identical equities and so either is OK.
The key to getting this problem correct is to pick the right game plan. Without the right plan you will go astray. It is vital for Red to keep the 5-pt anchor until there is more clarity as to how this game will develop.