Hello,
Please note that each chart type support only specific positions.
If you open MS Word and create a line chart, you can check the available positions for this chart type are the following: center, left, right, above (top), below (bottom).
Column chart supports the following positions: center, insideEnd, insideBase and outsideEnd.
Unfortunately, MS Word doesn't support all positions types for all chart types (https://c-rex.net/samples/ooxml/e1/Part4/OOXML_P4_DOCX_ST_DLblPos_topic_ID0EJ3QRB.html#topic_ID0EJ3QRB). And the bestFit value is not supported in most cases (and may generate a corrupted document).
For your task, maybe the best approach is adding a supported position for each series (mixing them):
'theme' => array(
'serDataLabels' => array(
array(
'showValue' => 1,
'formatCode' => '#,##0.00',
'position' => 'top',
),
array(
'showValue' => 1,
'formatCode' => '##,##0.000',
'position' => 'bottom',
),
array(
'showValue' => 1,
'formatCode' => '#,##0.0000',
'position' => 'right',
),
),
),
Regards.