Most of the 平仮名【ひらがな】 characters have the 濁点【だくてん】 above the stroke but there are two cases where it is placed below the stroke:
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The position of a dakuten is not as strict as you think. It has to be placed near the top right corner, but it may be moved or rotated according to the font designer's choice. Here are some examples of voiced hiragana rendered with various fonts installed on my PC:
When you practice handwriting, please use shapes of a 教科書体 font (the blue one above).