After staring at the data a bit more:
Woodcutters are only valuable at low coal levels. At coal level 1 an extra miner is consistently more valuable than a woodsman
Brewers seem to be actively harmful to fort value.
There is a big fall in fort value when no warriors are present.
The previously observed drop off in the value of additional miners after 5 seem to occur because it makes it less likely for other valuable types to be present, not because it is intrinsically bad. 6 miners and 2 smiths/crafters seems to be much better than 5 miners and 3 smiths/crafters.
My final selection for the fort of Magh Loduhr is therefore:
4 farmers
6 miners
1 smith
1 crafter
1 warrior
Some traits definitely go better with some houses, however I couldn’t see much in the way of clear cut rules. I constructed the following highly provisional allocation by considering students that were sorted when the helm was still reasonably reliable, and then combining the probabilities of a student with each of the 5 ratings being sorted into each house, and selecting the one which on balance seemed most likely.
A Dragonslayer
B Thought-Talon
C Serpentyne
D Dragonslayer
E Humblescrumble
F Serpentyne
G Dragonslayer
H Humblescrumble
I Humblescrumble
J Thought-Talon
K Dragonslayer
L Dragonslayer
M Dragonslayer
N Dragonslayer
O Serpentyne
P Thought-Talon
Q Dragonslayer
R Humblescrumble
S Serpentyne
T Humblescrumble