under load there is some splay, so measure the BB height, that is the scale numbers in the legs,

add another 30mm , say.. , the rubber feet are good, put on the end, bigger footprint for soft soils.

I had discs of 1/4" aluminum deck plate,
welded on the bottom of mine, Back to back D shaped so fold is unimpeded.

the splay needed a bit more length, so the thickness helped too .. cut a skosh short.

best if you have a Kickstand Plate welded on the chainstays, the clamp compresses the tubes
as you keep tightening it as it rotates a bit , in use..