how to take shots 3 to 20 feet from barrel when scope is set 4 farther fx impact

i would like to hear your guys methods to aim for realy close shots with fx impact. i eat my back yard chickens and ducks every once and a while that my wife raises and use my .30 impact to dispatch them but usualy the shots are realy close and im sighted to 45 yards and further very accurate set up i did the long rangers 150 yard with it. my scope goes down to 5x and the hold over is alot for up close i will aim over there heads and long story short vital shots work well enoughf when you cant get hold over perfect but i was thinking about a mini red dot yesterday and today i notised under the picatini rail there is an opening you can look thrue with a groove the cheek rest is in the way but it looks like it lines up with the factory supressor maby ill glue a front sight post to the supressor tip and try it i would have to remove or modify cheek rest and aim from the but of the gun. but i would like to hear any tips you guys might have on close up accuracy with fx impact 
 
I have a different gun but the scope is set very high over the barrel also making close shots very difficult. I was thinking of puting a red dot scope on a 45 degree angle off the rail and sighting it in for the really close shots. But right now i just set my power to 4X and put targets evey 5 feet and sight in with the correct mildot holdover and made a range card that i attached to the stock with a Football quarterback wrist playcard band. Works like a charm. You can see it on the picture. Sorry if this is not what you were thinking. Let me know what you do so i can try it too.

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the range card would probably be the most accurate solution ill try to make one when i get a chance, some day i might buy a mini red dot and give that a try. for now i tried tilting it and pointing by looking along barrel but theres a picatini rail there that was stilll more accurate than looking thru hole under top picatini rail thanks for the tips guys