When you say you take laps one and two very easy, how fast do you go out? A true 1600 effort shouldn’t feel easy at any point past the first lap and should just get increasingly harder from there.
You need to find out what kind of runner you are, sprinter, mid d or long d. What are your strengths? I am speed based and always will be so I usually run the first 400 hard, I actually go out at goal pace (maybe a sec per lap faster) to get myself really in the zone. I float the next two laps at a sustainable yet considerably painful pace and the last 400 I absolutely kill myself (I save some of my mid-race energy for this as speed and kick are my strength). As a lofelong sprinter with limited aerobic ability, te easiest way for me personally to get te fastest possible time is by dominating lap #1 and lap #4 and let laps 2-3 be what I would call a painful recovery but you may find that you race very, very different,y. In fact, most people don’t race like I do. IF you were to try my racing stategy, I am not suggesting you blast a 80 sec first lap, run the next two laps at 8:30 pace then blast the last lap in 90 or something stupid like that. I mean more along the lines of go out at 90 sec, float the next two and try and get yourself in the flow and zone at say maybe 6:30 pace then blast the last lap at sub 6 pace.