Array formula wierdness. Unexpected result

[Russk68]

Hi All
I am using the following array formula in BY2:
{=IFERROR(INDEX($AD$2:$AD$2199,SMALL(IF(($AC$2:$AC$2199=$B$4)*($AE$2:$AE$2199=$AA$1),ROW($AC$2:$AC$2199)-ROW(INDEX($AC$2:$AC$2199,1,1))+1),$AB2)),"")}

This is what the columns look like. The array formula is dragged down column BY. Column AB is a reference row for the formula.
I can not figure out why 1.7 does not appear in column BY. Column AD is formatted as General.
File is attached. It's the yellow sheet "Opto"
Any help would be greatly appreciated!

______AB____AD_____BY
1_____""_____""______""
2_____1_____1.1____1.1
3_____2_____1.2____1.2
4_____3_____1.3____1.3
5_____4_____""_____1.4
6_____5_____1.4____1.5
7_____6_____1.5____1.6
8_____7_____1.6____1.8
9_____8_____1.7____1.9
10____9_____1.8____1.10
11____10____1.9____""
12____11____1.10___""
13
14

[protonLeah]

(How to) Upload a Workbook directly to the Forum
(please do not post pictures or links to worksheets)

• Click Advanced next to Quick Post button at the bottom right of the editor box.
• Scroll down until you see "Manage Attachments",
• Click the "Choose" button at the upper left (upload from your computer).
• Select your file, click "open", click "upload"
• Once the upload is completed the file name will appear below the input boxes in this window.
• Close the Attachment Manager window.
• Click "Submit Reply"

Note: Please do not attach password protected workbooks/worksheets
Ensure to disable any Workbook Open/Autorun macros before attaching!

[FDibbins]

Without anything to test again.....
=IFERROR(INDEX($AD:$AD,SMALL(IF(($AC$2:$AC$2199=$B$4)*($AE$2:$AE$2199=$AA$1),ROW($AC$2:$AC$2199)),rows($A$1:A1))),"")

[JohnTopley]

You test AE against AA1 which has value 1. AE for AD=1.7 has value of 3.