Delete works different with different tools

[biuro74]

Thank you for reply.

I was reading that link, reading and still had no clue how to bind that technique to my case.
Tried google some YT solutions and accidentally found something really quick, easy and working: alpha to selection, shrink, invert, delete.
https://www.youtube.com/watch?v=wchU1_skBwU
Maybe someone will find this helpful as well.