FFS...is this really 2009? I feel as though I have stepped into a time warp!
OP, YANBU, and I certainly don't think you deserve some of the vitriol your post has attracted.
Having been in a shared care situation for the last 18 months almost, I can understand your desire to spend more time with your DC.
My experience - & without wishing to hijack your thread! - is that when I left my Ex (because I had met someone else) Ex refused to agree to let me take the DC unless I could prove he would have them 50% of the time. As he starts work v early in the morning, the only way we could equally split care (he insisted the 'time' we had with DC was 24 hours ie including when they were asleep) was for him to have them every weekend. Which I agreed to because at the time I felt I had no alternative.
I've asked him to negotiate over this many times since I left. He has flatly refused. He also still cannot forgive me for not wanting to be with him, tried many times to win me back, has told me I am never to let another man near 'his' DC or he will kill him, and so on
Whilst my arrangement is obviously different to yours, I can entirely empathise with agreeing to something because you think its best at the time for DC, avoids further argument, courts etc, and because - if you're like me - you think that your EX will eventually be more reasonable, & you will be able to re-negotiate.
Sadly it doesnt always work like that.
I think mediation is key here; it is so difficult when you both become entrenched in your positions to see any way forward. To be honest, an arrangement which allows some weekend and week time for both parents, if workable in terms of jobs and living arrangements would be best all round. I think therefore if there is any way you can move a little closer that should help matters as well.
I really do hope you are able to work out a fairer split