I think A8.22 in combination with 8.26 EX2 is pretty dang clear. There aren't residual attacks for simultaneous expenditure, moreover simultaneous versus separate expenditure isn't even the principal issue.
A8.22 ...A unit can be attacked by Residual FP only once per Location [EXC: if, since that first Residual FP attack, the Residual FP has increased in strength or the unit is subject to more-negative-DRM/less-positive-DRM, it will be attacked again by that Residual FP upon further MF/MP expenditure]
In the 8.26 EX2. we have a unit entering a OG hex containing Residual and a foxhole. Entering the hex costs 1 MP, it undergoes a residual attack and then makes a separate MF expenditure to enter IN the foxhole. A foxhole is of course still the same location and the unit does not undergo a second Residual attack.
It's a two squad foxhole, and there's another squad in there. On its Mph it recovers an MG in the foxhole (1 MF expenditure) and takes attack from the residual. The example concludes saying that if the squad: "then exits the foxhole, it would be attacked again by the Residual FP
since it is becoming more vulnerable with a -2 DRM for FFNAM/FFMO."
Which is to say
not since it is expending further mp.
Residual FP does not attack moving units as if it were a DFF unit making a small arms attack at every possible MF expenditure. Residual FP is not a DFF'ing unit.