Your body has that much lean because it needs it to support the weight you have on your body now. But at a lower weight, it wouldn't need as much muscle.

At this point, it's way too early to know what your ideal is. You might find you gain muscle, or lose muscle. I'll venture to guess you will lose muscle.

Just because it's ideal that our bodies don't lose muscle, doesn't mean they won't. And obviously someone closer to their ideal weight in the first place has less to worry about.

I think aiming for the goal your trainer set up for you is a wonderful plan. Have your BF analyzed every 20 lbs or so and recalculate and see where you stand at that time.

And remember they are not even close to 100% accurate. Your BF and lean fluctuates so much depending on how much is in your gut and how hydrated you are at the time.

I'm guessing you are starting a weight training workout. Good luck getting fit. Being male you have a great advantage and should look real buff in a year.

Also, there are sites online where you can estimate your BF. Here's one I use http://www.biofitness.com/abodyfat.html
And you can find others by searching. It might reassure you to see if they are similar or totally way off. I did mine a 2nd time at the above mentioned site, and it shows that I've lost 2 lbs of muscle (not good) but I'm not exercising either. But inches are lost and it shows my target weight closer to what I expect.