While 6 bit encoding is definitely a more efficient way to transmit the data, when it comes to stuff like this transmission speed is rarely a consideration. In high profile tournaments, players may have several hours each during a game (for example, the game in which Niemann is alleged to have cheated used a time format of 2 hours for the first 40 moves, +1 hour upon reaching move 40, and +30 seconds after completing every move after the 40th. Across 2 players, and assuming they make the 40th move, that's a 6 hour game total).

So when it comes to things like this, the main considerations are accuracy in transmission and comprehension of the message. If the player has to compute from binary to the board (which is an albeit really easy skill), there is still a chance that they can misinterpret the data. For this reason, most formerly caught "at the board" cheaters have used the simple "count columns, count rows" method.

More complex cheaters (who do not use an accomplice) have in the past gone to the washroom to find a stashed chess computer, plug in the position, see what the computer thinks, and come back.

Even amongst some top players, it's not uncommon for someone to play a move and then go to the washroom for up to 30 minutes and come back to see how their opponent responded. I mention this to further emphasize that 1) spending a really long time not making a move is relatively common and 2) while most cheating does occur in longer periods of thought, that in itself is not an indicator for cheating.

As for your mention of sending information, it can be a lot simpler than what you proposed. Since this method requires a relatively unrestricted view of the board, it is more than likely they will also be able to see the player, making physical signals a far easier method of communicating "HELP!!!" than becoming a kegel master. You could organize before hand something like "if I run my left hand through my hair and shake my head, I need help", and upon seeing this the accomplice could transmit the piece location.

And my theory about the butt plug being able to be smuggled through a metal detector is not based in a proven fact, but rather the assertion that if you could get one through a metal detector, which may or may not be possible, there would be no other checks in place to prevent a player from entering a hall with one.