Q:

Why SVG shadow is cut on the bottom side

I've made a little SVG icon that requires a shadow on the bottom. The thing that I couldn't understand is why its shadow is cut? 
Thanks in advance!

<svg xmlns="http://www.w3.org/2000/svg" class="default___3oPC0 barMiddleSVG___3x9T-" filter="" fill="url('#star_container_gradient_one')" stroke="transparent" stroke-width="0" width="43" height="36" viewBox="0 -1 43 38"><linearGradient id="star_container_gradient_one" gradientTransform="rotate(90)">
<stop offset="0" stop-color="#c2c2b3"></stop>
<stop offset="1" stop-color="#dedece"></stop>
</linearGradient>
<defs>
<style>.romb_top_border, .romb_bottom_border { fill: transparent; stroke: #e9ebd8; stroke-width: 1.5px; }</style>
<filter id="romb_container_shadow_bottom">
<feDropShadow dx="0" dy="2" stdDeviation=".5" flood-color="#4a444494"></feDropShadow>
</filter>
</defs>
<path filter="none" d="
            M 1 11
            L 21.4 1
            L 42.8 11
            L 42.8 26
            L 21.4 36
            L 1 26
            L 1 11
            Z
          "></path><path class="romb_top_border" filter="none" d="
            M 1 11
            L 21.4 1
            L 42.8 11
          "></path><path class="romb_bottom_border" filter="url(#romb_container_shadow_bottom)" d="
            M 42.8 26
            L 21.4 36
            L 1 26
"></path></svg>

A:

Couple things. Adjust your size of the svg to accommodate the size needed for the result of the filter on the svg element and it's viewbox, and increase the height of the filter to accommodate the boundary of the svg. Example below, hope it helps, cheers.
Oh, and PS, I assume the 8 digit hex color Mr. Longson pointed out is a remnant habit from say XAML Path habits wherein you can specify the alpha channel by appending a value to the first octet. AKA <alpha opacity>RGB?

svg { border: rgba(255,0,0,.2) 3px solid}
<svg xmlns="http://www.w3.org/2000/svg" class="default___3oPC0 barMiddleSVG___3x9T-" filter="" fill="url('#star_container_gradient_one')" stroke="transparent" stroke-width="0" width="43" height="40" viewBox="0 0 43 38"><linearGradient id="star_container_gradient_one" gradientTransform="rotate(90)">
<stop offset="0" stop-color="#c2c2b3"></stop>
<stop offset="1" stop-color="#dedece"></stop>
</linearGradient>
<defs>
<style>.romb_top_border, .romb_bottom_border { fill: transparent; stroke: #e9ebd8; stroke-width: 1.5px; color }</style>
<filter id="romb_container_shadow_bottom" height="150%">
<feDropShadow dx="0" dy="2" stdDeviation=".5" flood-color="#4a444494"></feDropShadow>
</filter>
</defs>
<path filter="none" d="
            M 1 11
            L 21.4 1
            L 42.8 11
            L 42.8 26
            L 21.4 36
            L 1 26
            L 1 11
            Z
          "></path><path class="romb_top_border" filter="none" d="
            M 1 11
            L 21.4 1
            L 42.8 11
          "></path><path class="romb_bottom_border" filter="url(#romb_container_shadow_bottom)" d="
            M 42.8 26
            L 21.4 36
            L 1 26
"></path></svg>

