I blindly tested different options before I came to patch size. I’ve used Inpaint for my work before and had to get satisfactory results after a long time of trial and error. 
And then I read the tutorial of @patdavid what @afre mentioned. However, the patch based Impaint that Pat describes in his tutorial is very time consuming, and I then experimented with Multi scale Impaint for your example.
I agree with you. I think that’s a pity too. GMI’C has high quality filters with great potential that can’t be fully exploited because they’re not well documented or there are no good tutorials for them.
A good example of how to make it outstanding is new denoising filter from @Iain.
Filter is very promising and @Iain has made an excellent and detailed video explaining it:
