Попробуйте использовать это.
Я нарисовал в Sketch
с радиусом угла 25
<vector xmlns:android="http://schemas.android.com/apk/res/android"
android:width="24dp"
android:height="24dp"
android:viewportWidth="250"
android:viewportHeight="235">
<path
android:fillColor="#00000000"
android:fillType="evenOdd"
android:pathData="M239.887,125.879C242.736,120.656 242.736,114.344 239.887,109.121L189.522,16.774C186.455,11.152 180.563,7.654 174.158,7.654L75.842,7.654C69.437,7.654 63.545,11.152 60.478,16.774L10.113,109.121C7.264,114.344 7.264,120.656 10.113,125.879L60.478,218.226C63.545,223.848 69.437,227.346 75.842,227.346L174.158,227.346C180.563,227.346 186.455,223.848 189.522,218.226L239.887,125.879Z"
android:strokeWidth="15"
android:strokeColor="#008000" />
</vector>
с 30:
<vector xmlns:android="http://schemas.android.com/apk/res/android"
android:width="24dp"
android:height="24dp"
android:viewportWidth="248"
android:viewportHeight="235">
<path
android:fillColor="#00000000"
android:fillType="evenOdd"
android:pathData="M237.581,128.273C241.244,121.558 241.244,113.442 237.581,106.727L189.943,19.38C186.001,12.151 178.424,7.654 170.19,7.654L77.81,7.654C69.576,7.654 61.999,12.151 58.057,19.38L10.419,106.727C6.756,113.442 6.756,121.558 10.419,128.273L58.057,215.62C61.999,222.849 69.576,227.346 77.81,227.346L170.19,227.346C178.424,227.346 186.001,222.849 189.943,215.62L237.581,128.273Z"
android:strokeWidth="15"
android:strokeColor="#008000" />
</vector>
С 40:
<vector xmlns:android="http://schemas.android.com/apk/res/android"
android:width="24dp"
android:height="24dp"
android:viewportWidth="246"
android:viewportHeight="235">
<path
android:fillColor="#00000000"
android:fillType="evenOdd"
android:pathData="M233.97,133.061C239.26,123.362 239.26,111.638 233.97,101.939L191.786,24.592C186.091,14.15 175.147,7.654 163.253,7.654L82.747,7.654C70.853,7.654 59.909,14.15 54.214,24.592L12.03,101.939C6.74,111.638 6.74,123.362 12.03,133.061L54.214,210.408C59.909,220.85 70.853,227.346 82.747,227.346L163.253,227.346C175.147,227.346 186.091,220.85 191.786,210.408L233.97,133.061Z"
android:strokeWidth="15"
android:strokeColor="#008000" />
</vector>
С 50:
<vector xmlns:android="http://schemas.android.com/apk/res/android"
android:width="24dp"
android:height="24dp"
android:viewportWidth="244"
android:viewportHeight="235">
<path
android:fillColor="#00000000"
android:fillType="evenOdd"
android:pathData="M230.359,137.849C237.277,125.165 237.277,109.835 230.359,97.151L193.628,29.804C186.181,16.15 171.87,7.654 156.317,7.654L87.683,7.654C72.13,7.654 57.819,16.15 50.372,29.804L13.641,97.151C6.723,109.835 6.723,125.165 13.641,137.849L50.372,205.196C57.819,218.85 72.13,227.346 87.683,227.346L156.317,227.346C171.87,227.346 186.181,218.85 193.628,205.196L230.359,137.849Z"
android:strokeWidth="15"
android:strokeColor="#008000" />
</vector>