IMHO that's a lot of volume to push through a 30g 5/16" pin. It can work but 28g 1/2" is probably better for you. The problem is likely not the pin though, but stomach injections - they've always been somewhat uncomfortable for me. Have heard from other guys on the forum that don't like them either.
My favorite SubQ spot by far is the fat pad on the side of my hip/glute. When sitting on the toilet, take your right hand and put the tip of your right thumb on your iliac crest and the tip of your index finger below it on your greater tronchanter. Reach back with your middle finger between your index finger and thumb towards your butt - the tip of your middle finger will be in a meaty fatty area. Pinch fat, inject there. On EOD, I go back and forth right side, left side every other day.
45 degrees is too much angle in that location unless you're really skinny - I've found if I inject larger volumes of oil at too steep of an angle, I get bumps/welts. With 5/16" pins I go straight in - with 1/2" I go on a slight angle.
After you've injected the entire volume of syringe, hold it there with the needle still in you for 10 seconds, then remove the needle. This seems to help minimize any leakage of the oil.
Good luck man. You'll figure out what works best for you. Trial and error.