Halving combat strengths

[Blackcloud6]

In PG 4th Edition, how many times do you halve combat strengths?  Only once or for each reason?  For example a 7-4 HMG is disrupted and attacks alone in assault.  Is its combat strength 4 or 2?

I may be having rules confusion with another game but I seem to recall you only halve once regardless of the number of times it is called for but I'm not finding it in the rules.