Worked well on seat stays and I used some electrical tape to protect the frame. Although the tape left some sticky glue residue when I took them off. Qq
Nice and utilitarian. Can't make out if you've used P-clips on the fork tubes?
Velo Orange have those mudguard stay mounts which I considered but they don't look strong enough for even a lightly loaded rack.
This was mine when I had a rear rack mounted. Held up my bag no probs.
Not sure if you got an answer but I used this tubus clamp set on my Steamroller as while back with decent results:
https://www.sjscycles.co.uk/carriers-racks/14mm-tubus-clamp-set-rack-eyes-for-seat-stay-mounting/
Worked well on seat stays and I used some electrical tape to protect the frame. Although the tape left some sticky glue residue when I took them off. Qq