I̶ ̶m̶i̶g̶h̶t̶ ̶b̶e̶ ̶m̶i̶s̶s̶i̶n̶g̶ ̶s̶o̶m̶e̶t̶h̶i̶n̶g̶,̶ ̶b̶u̶t̶ ̶I̶ ̶t̶h̶i̶n̶k̶ ̶e̶a̶s̶y̶ ̶4̶ ̶i̶s̶ ̶u̶n̶s̶o̶l̶v̶a̶b̶l̶e̶.̶ ̶T̶h̶e̶ ̶b̶o̶t̶t̶o̶m̶ ̶6̶ ̶c̶a̶n̶n̶o̶t̶ ̶e̶x̶t̶e̶n̶d̶ ̶u̶p̶w̶a̶r̶d̶ ̶o̶r̶ ̶i̶t̶ ̶b̶l̶o̶c̶k̶s̶ ̶t̶h̶e̶ ̶4̶,̶ ̶a̶n̶d̶ ̶i̶f̶ ̶i̶t̶ ̶g̶o̶e̶s̶ ̶h̶o̶r̶i̶z̶o̶n̶t̶a̶l̶,̶ ̶t̶h̶e̶ ̶6̶ ̶o̶n̶ ̶t̶h̶e̶ ̶r̶i̶g̶h̶t̶ ̶i̶s̶ ̶u̶n̶p̶l̶a̶y̶a̶b̶l̶e̶.̶

https://linjat.snellman.net/#game.easy.4

edit: My logic parts are weak