Here's a little table I think I've posted before, but I'll post it again anyway. It shows the records of each position of finish in the AL and NL from 1901-1960, sixty years in which both leagues were constant in size at eight clubs in each.
Code:
NATIONAL LEAGUE, 1901-1960
W L Pct HW HL HPct AW AL APct W% PctDiff
1st 5813 3317 .6367 3063 1528 .6672 2750 1789 .6059 4.79 .0613
2nd 5386 3740 .5902 2869 1702 .6277 2517 2038 .5526 6.35 .0751
3rd 5100 4003 .5603 2746 1830 .6001 2354 2173 .5200 7.11 .0801
4th 4766 4348 .5229 2606 1964 .5702 2160 2384 .4754 9.05 .0949
5th 4418 4671 .4861 2419 2124 .5325 1999 2547 .4397 9.54 .0927
6th 4030 5076 .4426 2209 2341 .4855 1821 2735 .3997 9.70 .0858
7th 3687 5390 .4062 2021 2457 .4513 1666 2933 .3623 11.11 .0891
8th 3222 5877 .3541 1806 2737 .3975 1416 3140 .3108 12.26 .0867
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TOTAL 36422 36422 .5000 19739 16683 .5420 16683 19739 .4580 8.39 .0839
AMERICAN LEAGUE, 1901-1960
W L Pct HW HL HPct AW AL APct W% PctDiff
1st 5814 3275 .6397 3150 1420 .6893 2664 1855 .5895 7.75 .0998
2nd 5378 3714 .5915 2914 1640 .6399 2464 2074 .5430 8.18 .0969
3rd 5078 4032 .5574 2778 1793 .6077 2300 2239 .5067 9.03 .1010
4th 4755 4326 .5236 2580 1978 .5660 2175 2348 .4809 8.10 .0852
5th 4451 4622 .4906 2424 2109 .5347 2027 2513 .4465 9.00 .0883
6th 4086 4991 .4501 2263 2259 .5004 1823 2732 .4002 11.17 .1002
7th 3689 5396 .4061 2074 2452 .4582 1615 2944 .3542 12.85 .1040
8th 3104 5999 .3410 1731 2790 .3829 1373 3209 .2997 12.29 .0832
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TOTAL 36355 36355 .5000 19914 16441 .5478 16441 19914 .4522 9.55 .0955
Chart legend:
W is the aggregate total of wins posted by clubs finishing in that position.
L is the aggregate total of losses posted by clubs finishing in that position.
Pct is the overall winning percentage for each W-L record.
HW is the aggregate total of home wins posted by clubs finishing in that position.
HL is the aggregate total of home losses posted by clubs finishing in that position.
HPct is the winning percentage for each HW-HL record.
AW is the aggregate total of away wins posted by clubs finishing in that position.
AL is the aggregate total of away losses posted by clubs finishing in that position.
APct is the winning percentage for each AW-AL record.
W% is the actual number of wins at home divided by the number of predicted number of wins at home as calculated by the overall winning percentage. The result indicates the percentage of wins at home above what would be predicted based on the overall record. For example, a W% of 5.0 indicates that a team won 5% more games at home than it's overall winning percentage suggests it should have won.
PctDiff is the difference between the HPct and the APct.
We can see from the chart that over the sixty year period teams finishing in first had on average a .6367 winning percentage in the NL and a .6397 winning percentage in the AL.
The figures to note are the PctDiff figures for each position of finish. The NL shows something of a bell curve while the AL is more varied. Note how last place teams derive the biggest benefit in terms of W% from home field advantage due to them have fewer wins overall so each additional win gained at home is naturally a greater percentage of the whole.
It's also interesting to see a difference between the two leagues. The NL teams on average posted a home winning percentage .0839 better than the away winning percentage, which works out to almost 8.4% more wins at home. The AL showed a .0955 better home winning percentage, or almost 9.6% more wins at home than the overall winning percentage would suggest it should have. In the early decades of the AL the difference was quite pronounced, but as the years go on the spread narrows.
Given all this, it's obvious that there are a lot more factors at work than just a club tailoring its players to the particulars of its home parks.