Boolean only works on one foot

Hey folks,

i hope you can help me. English is not my first language, so if i am mixing up any words please ask and/or let me know.

I am trying to use the boolean-modifier to get imprints of the Dragons feet in the Rock underneath for easier positioning/glueing after printing. All used parts are repaired using the prusa slicer. First picture is the rock structure without any imprints:

https://preview.redd.it/54ubtgpnksge1.png?width=867&format=png&auto=webp&s=daf1fff7fc5b1c5066ead39180bad88f58efabcb

After positioning the Dragon on the rock with deliberate overlap (the undersides of the feet lay completely "inside" the rock structure):

https://preview.redd.it/u8baqeftksge1.png?width=762&format=png&auto=webp&s=42ed1fab8d8af1387a0b231e85c9ecc581b0c893

After using the boolean-modifier without any conscious changing of any options, there is only one foot imprint, though:

https://preview.redd.it/xoqejkj8lsge1.png?width=772&format=png&auto=webp&s=11d781eb04390e584038b3b8e7ee4ca99cc60fdf

I have tried back and forth but IIRC it only ever worked on the one foot without any obvious hint regarding the cause. The feet do look similar to me:

https://preview.redd.it/79qpfpejlsge1.png?width=676&format=png&auto=webp&s=39536a07f795ea81a49133c0dd54c7190f673d6b

The rock structure itself has about 50.000 vertices, the dragon has about 1.400.000 vertices if that is of any importance for you all.

I am sure that i am just not seeing the presumably very easy solution to my problem and it is driving me insane...Thanks in advance for any tips and help!

(Blender Version 4.3.2)