I can't make sense of your question, so here is a demonstration....

I can't make sense of your question, so here is a demonstration. If this is the depth during the auction:

	Column 1	Column 2	Column 3	Column 4
1	Bid Volume	Bid	Ask	Ask Volume
2	10,000	12.5	11	7,000
3	5,000	12	11.5	4,000
4	12,000	11.5	12	6,000

Then the match will occur at 12c, and there will be 15,000 shares traded. After the match, there will be 12,000 shares bid at 11.5, and 2,000 remaining at 12,000.

If, prior to the match, I bid 2,000 shares at 13c, the match will still occur at 12. If I bid 2,001 shares at 13c, the match will be at whatever is behind that 12c offer (presumably 12.5c).

See what difference one share makes?