Warrior Ancient and Medieval Rules

[Matt Kollmer]

Hope this isn't a dumb Question(Translate, don't think even less of
me!)
My assumption is that *Any* army which can upgrade EHC to SHC can mix
them into one unit of front rank SHC, back EHC as long as they are the
same troop type on the "same line" in the list.
Is this assumption correct? or just make an ass of me?
Where could this rule be found in writing in an attempt to defend
myself later?

just tryin to get it right
Matt