Im just curious.
Personally, I feel like the 6x7 board doesnt provide enough space to manage unit piece properly in the latter part of the game. Let me give an example, one game i was facing against an opponent who is playing purely assassins. I managed to win against his board when i finally purchased Yasao since he benefits from being alone. The other action i have taken is shifting all my other pieces in front of my opponent's pieces in order for them to prioritize Yasao instead of my other pieces. Once my opponent realized what was happening, he created a horizontal hook shape with his assassins on the board, making it impossible to rearrange my pieces accordingly. I ended up losing from 92hp to zero
Playing other Autochess style games, majority of them use an 8x8 board. The extra line allows for piece to be either dragged forwards for aggression or back to allow the opponent's pieces to spread out, you get the idea.