CUP: the three-cell path
Trace CUP through 1 at row 5, column 5; 2 at row 5, column 4; 3 at row 4, column 4. Those cells read C → U → P in path order. Start at the C, move one cell left to U, and then turn upward to P.
This route uses one left move and one up move, producing one turn and two straight segments. It spans two rows and two columns, visits the board edge twice, and includes one corner visit. Its starting cell has two open orthogonal neighbors, while its ending cell has three.
Placed first, this path assigns three open cells and leaves 18. Its compact shape gives you a precise early check: the letters, both orthogonal moves, and the single change of direction must all agree before you reserve those cells.