well we don’t have any depth info but you can go down to 1mm or 1/32" if the length of cut will accommodate the corner. If you have an engraving bit (V bit with about a 20 degree angle) that might get in there.
As long as the back is square at the ends of those profiles. Looked like an undercut when I looked before. As long as it’s not you’re right.
Either way, the larger the radius on the design, the easier to machine. Internal and external.
My advice if you open up the corners and that bit is square would be to program a good finish pass and also use it to rough. That can save you programming time/skill since machine time is probably a non issue. Simply just let the same pass run but then -z.050” each time until you’re at depth. Obviously starting close to max depth above. That way you maintain a parallel path on all passes and then your final finish could be just .010-.015. If you opti rough and then finish, the cutter engagement may change and that blemish could be visible on the final casting. Doing this with a lowered singular path until final depth will help ensure a great surface finish and also be easy on the machine and your head lol
There aren’t any undercuts and the max depth for each half of the mold is 14.5mm. This is also going to be a lead fishing lure/weight, so while finish doesn’t have to be perfect, it should be as smooth as possible given the desire for smooth hydrodynamics in use.