front end - What governs images resizing in the FrontEnd environment

What is responsible for the middle Row images' size? And why single image row is different?

{#, Row[{#, #}], Row[{#}]} & @ RandomImage[1, {100, 100}]

I know I can prevent that with mapping with Pane but I would like to have more understanding about what happens.

I thought it is related to some styles but I haven't found anything related in Core.nb under ImageGraphics or RowDefault styles.

There are related options like ImageSizeAction or ImageSizeMultipliers but I've failed to find connection with the case.

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It doesn't seem predictable, since here overall size is larger yet nothing is resized:

{#, Row[{#, #, #, #, #}], Row[{#}]} &@RandomImage[1, {50, 100}]