The link in your question is good, but it needs to be adjusted as follows.

=IFERROR(INDIRECT("B"&SMALL(IF(X25=$D$17:$D$22;ROW($D$17:$D$22);"");ROW($D$17:$D$22)-16));"")

Enter as an array formula {} by pressing Ctrl+Shift+Enter. The result is 4, 5, and 6 as you requested.

Adjustments:

• INDIRECT("B"& — In your case, you want the value from column B, not the index.
• X25= instead of "a"= because you want the value from that row.
• ROW($D$17:$D$22)-16 instead of ROW()-2 because the row number is from the D column, not from the location where you're putting the formula.

EDIT:

The OR function itself will not work in an array formula, so use the + operator instead.

=IFERROR(INDIRECT("B"&SMALL(IF((X25=$D$17:$D$22)+(X25=$E$17:$E$22);ROW($D$17:$D$22);"");ROW($D$17:$D$22)-16));"")

Result: 2, 3, 6

The link in your question is good, but it needs to be adjusted as follows.

=IFERROR(INDIRECT("B"&SMALL(IF(X25=$D$17:$D$22;ROW($D$17:$D$22);"");ROW($D$17:$D$22)-16));"")

Enter as an array formula {} by pressing Ctrl+Shift+Enter. The result is 4, 5, and 6 as you requested.

Adjustments:

• INDIRECT("B"& — In your case, you want the value from column B, not the index.
• X25= instead of "a"= because you want the value from that row.
• ROW($D$17:$D$22)-16 instead of ROW()-2 because the row number is from the D column, not from the location where you're putting the formula.

EDIT:

The OR function itself will not work in an array formula, so use the + operator instead.

=IFERROR(INDIRECT("B"&SMALL(IF((X25=$D$17:$D$22)+(X25=$E$17:$E$22);ROW($D$17:$D$22);"");ROW($D$17:$D$22)-16));"")

Result: 2, 3, 6

Regarding your other comment, it's not directly based on the size of the source — the resulting array is actually that big, only some of the results are empty strings ("" in the formula). You could add a filter to hide empty results by selecting column Y, going to Data > Auto Filter and unchecking (empty).

The link in your question is good, but it needs to be adjusted as follows.

=IFERROR(INDIRECT("B"&SMALL(IF(X25=$D$17:$D$22;ROW($D$17:$D$22);"");ROW($D$17:$D$22)-16));"")

Enter as an array formula {} by pressing Ctrl+Shift+Enter. The result is 4, 5, and 6 as you requested.

Adjustments:

• INDIRECT("B"& — In your case, you want the value from column B, not the index.
• X25= instead of "a"= because you want the value from that row.
• ROW($D$17:$D$22)-16 instead of ROW()-2 because the row number is from the D column, not from the location where you're putting the formula.

The link in your question is good, but it needs to be adjusted as follows.

=IFERROR(INDIRECT("B"&SMALL(IF(X25=$D$17:$D$22;ROW($D$17:$D$22);"");ROW($D$17:$D$22)-16));"")

Enter as an array formula {} by pressing Ctrl+Shift+Enter. The result is 4, 5, and 6 as you requested.

Adjustments:

• INDIRECT("B"& — In your case, you want the value from column B, not the index.
• X25= instead of "a"= because you want the value from that row.
• ROW($D$17:$D$22)-16 instead of ROW()-2 because the row number is from the D column, not from the location where you're putting the formula.

EDIT:

The OR function itself will not work in an array formula, so use the + operator instead.

=IFERROR(INDIRECT("B"&SMALL(IF((X25=$D$17:$D$22)+(X25=$E$17:$E$22);ROW($D$17:$D$22);"");ROW($D$17:$D$22)-16));"")

Result: 2, 3, 6