1380 RMA, P1 = 8hrs???

Curious about how P1/P2 and hours worked/compensated are calculated on 1380s for RMA.

On the 1380 sheet it says P1 = 4hrs worked. Makes sense. P2= 8hrs, etc.

However, I was told by our HR civ who processes the 1380s that P1 = 8hrs worked for reservists, given how BA breaks down (1 MUTA = 1 "day" of pay = 8hrs outside of BA)

This doesn't jive with me. Can someone unravel this? Bonus points for reg refs.

(Chicken fries and those popper things, if I'm in the right spot)