[Rules] Who commands the SPAs?

[campsawyer]

(i) since nothing is said explicitly to the contrary, does one take the normal meaning to be that a regular leader with a combat bonus can activate any mix of SPAs and regular artillery pieces in one or two (depending on the leader's bonus) adjacent hexes to combine their BF values into a single attack value or ...

Sense you have pointed out in (i), nothing is specificed, but in (ii) you infer, then I would go with you first. The Golden Rule for rules as written, never read in more than is there and if it doesn't say you cannot, then you can.