Thank you HG, for that statistical confirmation of ~ 1/3 pawn. So what
creates that imbalance? 

Chief contrafactual, cont: The first change is pawn reversibility. In
chess, pawns and pawn chains are often hung out to dry when the opponent
breaks through the pawn wall. If pawns could move backward along their
file, they would be more able to defend. Increasing the defense of the
pawns this way should help black slightly more than white, given the
unbalanced won-loss statistics. It does not seem that it would play a major
role in what is a 30% win-loss advantage when draws are thrown out.

The second change is board length. The longer board, all other things being
equal, including the pawn double-step first move, will cause the pawns to
take longer to contact each other. This will act to give black easier
access to adequate maneuvering room for his pieces. One strategy is to
squeeze your opponent to death. Allowing more free space for maneuver,
especially while slowing down pawn contact, will allow black to improve the
defense, thus evening things up. The larger board does little to affect the
infinite sliders, however. Any sort of aggressive play by white, however,
would likely do much to negate this effect, so again, I don't see a major
role for either of these first two changes. Even the combination doesn't
appear to be that potent, pretty certainly providing less that half of the
total effect.

That leaves mobility as the last man standing. The reduction of the average
piece movement range to about 2 squares, on a board that is now 12 squares
deep, and with "pawns" that can retreat, certainly accounts for the
mechanics of the 30% edge white gets in won-lost only. And we've already
seen that the reversibility and the larger board, by themselves and
probably even in concert, don't seem to account for the discrepancy in
scores. 

If Chief is close enough to FIDE in concept, and it should be, because it
is played strictly as chess on an individual piece movement basis, the
analysis should hold. Each individual piece is moved in turn, and each move
must be legal when it is made. A slight restriction on what pieces may move
in any given turn shouldn't have any real effect, nor should the
multi-move aspect. You actually could play it moving 1 piece/turn/side, but
it would be one heck of a boring game.

Therefore, the reason white wins from first turn advantage is primarily and
probably overwhelmingly the mobility of the pieces. Can anybody knock this
argument down?