Every time i jump i don't fully extend my arms, sometimes i do, sometimes i don't. When i measure my standing reach it varies about 3in~, when i just reach, and when i try to reach my highest. Should i just practice extending my arms?

Also when i jump my arms are extended but they are a bit forward and not all upwards, is that a bad thing?

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Height: 5'6
Vertical: 31'-32'