i continued with the same stats as above and fought 4 more battles

results are 19 kills, 15 kills, 15 kills, 14 kills

i ran another test. because your tests confirmed that the shield value isnt added but distracted i also changed the feudal knigts stats. also because i feared that the melee stats may have been switched for missile stats i lowered those too.

Retinue (0 missile attack, 0 melee attack) Feudal (60 armour, 0 defense, 0 shield)

i only fought 2 battles because i thought the results are clear as it seems

1st battle: 15 kills
2nd battle: 9 kills

it seems that missile fire is totally random... its weird but not entirely gamebreaking