How to reinforce shower pan threshold?

The left rear floor corner is highest (the shower pan touches/sits on the floor), sloping down diagonally to the front right corner (lowest). The front right corner shim is 5/8", the left front corner is 3/8" shimmed, with shorter shims under left middle and right rear corner.
The pan perimeters are level and ready for the mortar to be applied to the underside. However, I don't know how to support the threshold flange, especially as the gap below it is a gradual wedge shape. I think that If the threshold is not properly supported, it would begin to crack as it is periodically stepped upon.

1. Should I form a mortar mini-curb to be vertically flush with the threshold to avoid trapping water on a 'step'.
2. Would forming a mortar mini-curb at that location not gradually wick water under the pan?
3. Would stepping on the threshold not eventually crack the mini-curb?

Advice here will be most appreciated.
Thank-you

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