[How to reduce mask in pixel]

Haha, wowzers - Gold (potentially)! I think I've earned rest of the day off Ancient post but if I got here looking for an answer then I figured other peeps probably do too.

Does seem weird that 7 years later Affinity Designer refine mask still won't let you -% trim however.

[How to reduce mask in pixel]

If it's any use for people also searching, I cmd/ctrl clicked my mask to make a selection, then in the top toolbar > Select there are more familiar refinement tools there. You can reduce the selection there and then create a new mask by clicking the mask icon in the layers panel

[Golden Canon Grid]

Thanks!