Calculating defense and attack

[Chimera]

I'm at level 6 with 3 allies and 30 units, 188 A & 285 D.
I purchased an AC, 27 A & 46 D.
I thought my new stats would be 215 A (188+27) and 331 D (285+46).
Instead my new stats are 208 A and 324 D.
What is it that I do not understand?
Thanks.

[Hassleham]

You have 3 allies so you'll take the best 12 units to battle. The AC will have replaced one of your other units, therefore you have 188 + 27 - whatever attack the other unit had, and 285 + 46 - whatever defence the other unit had.

[JMC]

You cant bring enough units into battle so right now every unit you buy will replace a different unit instead of giving you the full stat boost.

[Chimera]

Got it. Thanks.