I've been thinking of adding F11 and F12 (and F13) to the keys under `Del` on layer 3 (basically the same thing ED does by default on layer 1). As for the thumb block, that took me some time to work out because I thought hitting all those buttons would be easier than it is. So what you see is effectively my attempt to duplicate as many buttons in places that generally make them fit the combinations I need to hit when I need to hit them.

On the left side, `Cmd` is the first button because on a mac, that's the most important modifier key and that position is the "natural" position for my hands.

Next `enter` (or really on a mac, `return`) with the alternative function of being `Ctrl` if held down. I rarely need `Cmd + Ctrl` but those two are pretty big tagets and easy to mash together.

For the smaller buttons, the layer switch is accessible without a large hand shift, so that is why its in its position at the bottom.

Above I have `Option/Alt` and `Ctrl` above that. The idea is not to use those all that often, but to use them if I need `Ctrl + Alt` or need the `Alt` key and can't use the one on the right side for some reason. If I need to use these two in that position, I do usually have to look at the keys (though currently as I work through learning middlemak... I'm looking at the keys a lot anyway).

Finally `Del` is where it is mostly because it doesn't require a huge hand shift (though I usually press with my index finger instead of thumb), and I liked having a forward delete on a dedicated key. Again bearing in mind I'm used to typing on laptop keyboards/75% layouts, so my other usual is `Fn + Backspace` for a forward delete, so needing to shift my hand isn't a huge concern for me.

On the right side, the same thought went into laying things out in a way that made sense for my habitual modifier usage while being as redundant as possible. On the far right, space obviously, again in the position that's most "natural" to my hands.

Followed by another `enter/return` with again the alternate function, this time of `Option/Alt` when held. Having two enter keys isn't something I make a lot of use of (I don't alternate which hand is enter when typing for example) but it allows me to make use of that alternate functionality and still be able to hit enter with a modifier held down and no need to move my hands or find one of the harder to hit keys. `Option/Alt` takes this position because Ctrl has it on the other side and also because my most common `Option + ${key}` combos are `Option + Left/Right Arrow` for skipping by word and the arrows are on the other half so no weird hand contortions (and again, coming from a laptop, I usually did that with two hands anyway. Incidentally, this also means I can use the layer3 hold on the left hand, and option + the arrows in the letter cluster (ijkl on a qwerty layout) that I programmed into layer 3 if I really need to do a lot of arrowing around.

`Cmd` sits in the lower left because again, it's the most common modifier in macOS. I don't often need the left side one, but it gets more ease of access than ctrl because when I need it, I need it.

`Ctrl` sits above option and again, the aim here isn't to use it on its own. In this case, the position allows me to shift my thumb up slightly and easily hit a `Ctrl + Alt` key combination (and for that matter shifting left instead of up gives a pretty easy `Cmd + Option`

Lastly Pg Up/Dn are there because I like having dedicated buttons for them instead of needing a layer shift. I don't often use them during a typing session but more for paging through docs or reference material, so usually my hands are off the keys in the first place, and needing to look at them if I'm not finding it by quick feel isn't a huge problem for me.

I should also say this is probably by 5th or 6th iteration on those clusters and it will probably change more in the future. I'm slowly honing in to something that I really like, but it has taken some serious paying attention to what I actually do. My first attempt was a lot more "normal" with a row of modifiers in order, or my second attempt that put the modifiers all on the small keys and used the larger ones for more layer shifts (hence all the Cmd + Key items on layer 3). Turns out I'm not a huge fan of constantly switching layers, probably because I'm a terrible touch typist who on a regular qwerty keyboard mostly uses just 3 fingers on each hand so keeping my hands in one place and letting the keys "come to me" with layeer shifts feels wrong.