To be honest with you, the correlation betweent the outcome of Agassi and Sampras matches and the type of surface is not all that strong
1995 Final: Agassi won
2000 SF: Agassi won
OK, so the slower highbouncing surface used at the AO obviously favours Agassi more, but in both matches Sampras was in a winning position, and he was only two points away from winning in the 2000 SF before Agassi somehow pulls out the win.
Agassi leads 3-2.
Agassi marginaly leads the head to head on this surface, but at the FO I would always favour Agassi because of the best-of-five sets format which, because of the fact that surface suits Agassi's game more, increases the chanes of Andre winning. It is debateable how much you can read into the last two defeats of Agassi on clay by Sampras because they were minor tune-up events, but they nonetheless proved that Sampras could beat him on clay.
Sampras leads 2-0.
These were the only times they met on grass and they were both at Wimbledon: the first time was in the 93 QF when Agassi was defending champion, and Sampras only barely got past him in five sets, and the second occassion was a complete demolition in the 99 final, when Agassi was probably in the best form of his career.
Sampras leads 4-0
There 's no doubt that Sampras had his number here on this fast hard court: in the four meetings none of them went to four sets, and the 1990 final was a straights sets demolition.
Sampras leads 5-2
Sampras, not surprisingly, also has his number on the fast indoor surface of carpet.
CONCLUSION: Playing on slower, higher bounce surfaces like the AO and clay increased Agassi's chances of beating Sampras, but Sampras had a better chance of beating Agassi on these surfaces than Andre had of beating Pete on faster surfaces such as grass, fast hardcourt (USO). This is shown by the fact that Agassi only marginally leads the clay head to head, and because Sampras was in a winning position on both of their meetings at the AO- a type of hardcourt that favours Agassi more.
In contrast, a combined record on fast surfaces (grass, carpet, USO) of 11-2 to Sampras, shows that Agassi could barely make a dent on Pete's favoured surfaces, probably because it increased the number of points Sampras could win on hi first serve, and therefore prevent Agassi from taking control of the point from the baseline.