Is it better to defend the Army’s network in the field or from afar?

You need to defend a network at every access point. If you don't provide security at all levels you will have your network security compromised even from unsophisticated attacks.

In air conditioning.

Just as in garrison, you have gate guards, in the field, when you set up your network, you will need Cyber warriors to defend the network from adversaries who would seek to compromise it for various reasons. It makes sense that units will now need to ensure they have the support of 25Ds and 17Cs to protect those information systems.