I think batting Papi in front of Manny helped Papi, but it's harder to tell about Manny.
I could be wrong, but it looks like, starting in 2006, it was almost exclusively Papi 3rd and Manny 4th.
In 2003, when Papi was first proving himself as a beast, Manny batted 4th and Papi 5th (Nomar 3rd, mostly.)
1.014 Manny 4th
.983 Papi 5th
2004:
3rd
.993 Papi in 421 PAs
.972 Manny 217
4th
1.030 Manny in 445 PAs
.958 Papi in 229
(This seems to show Manny did better after Papi.)
2005
3rd
1.030 Papi in 566
.908 Manny in 142
4th
1.014 Manny in 505
.959 Papi in 145
Maybe, I'm wrong.
We don't know how many times the other guy was up before or after, but it looks like Manny did better batting 4th not 3rd.