Hey, George, it's been a while since we argued opposite sides of a
question. This seems like a fairly interesting one to kick around a little.
But I'd like to start by looking at some supersized games, or at least
game boards.

On a 12x16, there are 2 ways to orient the board. With 50% starting
density, the simplest setups for the 2 orientations are 3 rows of 16 per
side, or 4 rows of 12. Using the 10% rule, 192 squares gives 19 different
kinds of pieces. One to three pawns leaves 16 - 18 piece-types. We'd want
3 or 4 colorbound pieces, anyway, just because. Even with weak pieces, the
total power on board adds up when you start with 96 squares occupied. So
you want to mitigate some of it. Besides, there are some neat colorbound
pieces besides the bishop and the Omega wizard. I'd recommend John Ayer's
Duke, a colorbound queen-type slider as a third, and something like the
modern elephant [ferz + alfil] or another short-range leaper [but not the
camel by itself - that piece is just awkward, and should be restricted to
those games where it is designed in as an integral part of the game, like R
Wayne Schmittberger's Wildebeest Chess] of range 3 or so. 

That still leaves 13, give or take, pieces to go. The king leaves a dozen
or so pieces, and we've used up 4 colorbound pieces already. Well, what
sliders do we use? Bishop's already used, so we have the rook and queen -
down to 10. 

Let's hold onto the knight for a while, since it is so shortrange. We may
have to get creative here, but for now, I'll note the knight covers that
missing piece if there is only 1 type of pawn in the game, leaving 18 more
pieces to find.

Okay, I've kept you in suspense long enough, George; we can use the
falcon as a shortrange slider. I'd also recommend the nahbi, Uri Bruck's
sort-of knight analog, which slides 2 diagonally, then steps 1
orthogonally. It visits the 8 knight squares plus the 8 squares diagonally
out from those 8 knight squares. Now we're down to 8 pieces. 

Now I'm getting desperate. The BN and RN. The bent hero and shaman [and
adding 1 more colorbound, but strong, piece]. Four pieces to go... help. 

Four more piece-types to go, and that's if you like my choices so far. I
could see anybody knocking out maybe a half dozen of my choices. This is my
first move, arguing by counter-example. Or, if you prefer, arguing by
example. 

Enjoy.

ps: The original value I saw for the Mann [non-royal king, aka: guard,
prince...] was 4, so a 3.88 piece would be the mann without the straight
back move. However, HG Muller comes up with a much lower figure for this
piece, so add a second step forward only, or a forward-only dabbabah leap.
Or you could try dumping the mann's backwards move and adding the 2
forwardmost knight moves, either lame or not. It seems to me that for
pieces of less than rook value, you could play around with the mann [a
superset of gold and silver], knight, dabbabah, and alfil and pretty much
dial up a piece of a certain value. Of course, these pieces would very
likely be infuriating to use en masse.