Nighttime Corrections

I cant for the life of me figure out why our nightime corrections do not typically work. We are 6weeks into the pump, and I have learned ALOT to say the least. Our problem is the ISF of 400…certain. I can give Maddison .1 .2 .3 for 200’s or mid-high 200’s corrections all night, and they wont touch her. During the day she is good with these tiny corrections. So, you would say, change the ISF at night. NOPE! I have tried this several times…I would over-ride the pump and give .5 for say, a 280 and she would be at under 80 within an hour and a half! So, why would a .4 do nothing, but a .5 is too much (at night) .3, .2 doesnt budge…SOMETIMES a .4 will bring her down about 40pts…sometimes nothing…but a .5 is a guaranteed drop of at least 180 points any time of day. ???Hmmmm, Am I missing something?