Oldbayrunner:
Another consideration is St Andy's is a par 72 whereas Bethpage Black is a Par 70, therefore it takes a lower score on a par 72 to get lower than your average than on a par 70.
I'm sorry to say that this is not true.
Can't you read correctly...The OP shot a -3 over 18 holes on St Andy's, which is a par 72, equaling a 69 , if he shot a -3 on a par 70 would equal a 67, a two shot average difference, so therefore for him to shoot under his average on a par 72 course he would need to shoot a lower score than on a par 70. Therefore it takes a lessor score to shoot under ones average on a par 70 than a par 72.
All the rest of what you are saying is correct but read wtf I wrote correctly before you say I am wrong.
For the average only the gross scores count, a 70 is a 70 and a 72 is a 72. 9 hole scores are doubled, 33 => 66.
On a par 70 the same amount under would be a 64. A 64 would lower his average greater than a 66, so it would still take a shooting a lower score on a par 72 to equal the same amount of average lowering difference than a par 70.
P: Your average is well saturated (>25) as you have at least 200 combined TP stroke play and CTTH rounds in the score history.
Therefore you don't need to shoot below your average (though this certainly helps), but lower than the highest score in the calculation. This might be 69 for example, thus only lower scores change anything.
That said, the 69 on STA doesn't move anything. Alas, -6 on Bethpage (full round) is 64, well below the average (sic!) for a change of -0.2.
You just proved what I said with this, to equal a 64 he would need to shoot a -8 on a par 72 or -4 on a par 72 9 hole round. Therefore guess what he still has to shoot a lower score on a par 72 than on a par 70...doesn't he.
This result caused a change of the score sum by 0.2*25 = 5, thus eliminating a 69 (64+5) in the mix.
Now you need to shave off another 4 strokes from the calculation to become a Master.
Have fun!